JP2006178066A - Dry nonmagnetic toner for electrostatic latent image development and developing device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device which suppresses toner charge up at durable printing and does not cause toner flying-off in a machine due to reduction of charge amount while preventing toner adhesion to a developing roller. <P>SOLUTION: In the so-called hybrid system developing device using a nonmagnetic toner, the nonmagnetic toner has an external additive on the surfaces of toner particles consisting essentially of a binder resin and a pigment, the toner is obtained by externally adding both of a low resistance titanium oxide surface-treated with a titanate coupling agent and a high resistance titanium oxide as the external additive to the toner particles, the low resistance titanium oxide has a volume resistivity of 10<SP>1</SP>-10<SP>6</SP>Ω cm, and the high resistance titanium oxide has a volume resistivity of 10<SP>8</SP>-10<SP>13</SP>Ω cm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a dry nonmagnetic toner for developing an electrostatic latent image formed in electrophotography and a developing apparatus using the dry nonmagnetic toner, and more particularly to a magnetic component for holding a two-component developer composed of a nonmagnetic toner and a carrier. A dry non-magnetic material used in a hybrid development system in which a toner layer is formed on a developing roller from a developer held on the roller and the magnetic roller to form a thin layer, and development is performed with a gap between the developing roller and the photosensitive member. The present invention relates to a toner and a developing device using the toner.

  In general, in an electrophotographic method or an electrostatic recording method, it is formed by exposing a latent image carrier made of a photoconductive photosensitive member or a dielectric to a photosensitive member charged by corona charging with a laser, an LED, or the like. The electrostatic latent image is visualized using a developer such as toner, or the electrostatic latent image is visualized by reversal development to obtain a high-quality image. In general, as a toner applied to these development methods, a thermoplastic resin as a binder is mixed with a colorant, a dye as a charge control agent, a pigment, and a wax as a release agent, and kneaded, pulverized, and classified to obtain an average particle size. Toner particles having a diameter of 5 to 15 μm are used. Generally, inorganic fine powders such as silica and titanium oxide, and inorganic metal fine powders are added to impart fluidity to the toner, to control charging of the toner, and to improve cleaning properties. .

  In recent years, as a dry development method in various electrostatic copying systems in practical use, in particular, four development devices of cyan, magenta, yellow, and black have been installed, and multi-color development is performed on a conveyor belt or a recording medium via a photoreceptor. In a color electrophotographic apparatus that performs the above, a magnetic roller that holds a two-component developer composed of a non-magnetic toner and a carrier, and a thin toner layer is formed on the developing roller from the developer held on the magnetic roller. A hybrid development system that performs development with a gap between the roller and the photoreceptor is known.

Such a hybrid development method has been studied as a high-speed image forming method for a one-drum color superposition method for sequentially forming a plurality of color images on a photoreceptor. In this method, it is possible to form a color image with little color misregistration by accurately superimposing toner on a photoconductor, and has been attracting attention as a technique for improving color image quality.
However, in recent years, attention has been paid to a tandem method in which a plurality of photoconductors corresponding to the color of toner are used to form a color image in synchronization with the feeding of the transfer member and to superimpose colors on the transfer member. Although this method has the advantage of being excellent in high-speed performance, it has the disadvantage of increasing the size because the electrophotographic process members of each color must be arranged side by side.

As a countermeasure, there has been proposed a small tandem image forming apparatus in which a compact image forming unit is arranged by narrowing the interval between photoconductors of respective colors.
In a miniaturized tandem image forming apparatus, it is advantageous to use a vertical developing device in order to minimize the size of the image forming unit in the width direction. That is, it is desirable in terms of layout that the developing device is arranged in the upper direction of the photosensitive member.
Japanese Patent Application Laid-Open No. 2004-228561 proposes that the layout of the developing device and the transfer member can be efficiently stored inside the machine and stored compactly. In this case, the developing device and the transfer device need to be slid to be attached and detached. It tends to be complicated in structure.

  In the small tandem hybrid development system, there is a gap between the photoconductor and the developing sleeve, and since this is a non-contact development system, the carrier adhesion to the photoconductor and the photoconductor using a magnetic brush, which were the conventional two-component development system, are performed. There are no scratches and high image quality is possible. Further, a two-component method by mixing with a carrier is adopted as a charging method in the developing unit, and the toner can be quickly charged to a desired charge amount even in high density printing or continuous printing. In particular, it is effective for models with a small developer capacity due to space saving. However, on the other hand, in order to reduce the size, the developing roller inevitably comes to the lower side of the magnetic roller, so that the developer is easily subjected to stress, and embedding of the toner external additive in the printing durability becomes remarkable, and the toner Problems such as adhesion to the developing roller 4 due to charge up occur.

Here, the toner adhesion to the developing roller 4 due to charge-up will be described in detail. As shown in FIG. 1, in the case of a small tandem type page printer, toner having a desired charge amount is supplied from the magnetic roller 5 to the developing roller 4 between the magnetic roller 5 and the developing roller 4, and at the same time, the developing roller. The toner remaining on the developing roller 4 is collected without flying to the photosensitive member 4, and fresh toner is always supplied to the developing roller 4.
However, because of the layout aimed at downsizing, it is necessary to move the toner from the developing roller 4 to the magnetic roller 5 against the gravity in this portion. Therefore, when the toner is charged up, the mirror image force on the developing roller 4 is increased and development is performed. Stripping from the roller 4 to the magnetic roller 5 is not performed. By doing so, the same toner always stays on the developing roller 4, and further, charge-up is accelerated, causing the sleeve to adhere, leading to a decrease in developability.

As a countermeasure against adhesion to the developing roller 4, in Patent Document 2, a countermeasure against toner sleeve adhesion is taken by bias control of the developing roller 4 and the magnetic roller. However, in this patent document, a magnetic roller is provided so as to be in pressure contact with the developing roller. In addition, the developer to be used is also a one-component developer, which is not only different from the technical field of the present invention but also has no measures taken from the toner side.
JP 2001-91123 A JP 2001-109242 A

  In view of the problems of the prior art, the present invention reduces the toner charge-up at the time of printing durability in a hybrid developing system, particularly a small tandem type page printer, prevents toner adhesion to the developing roller 4, and further reduces the charge amount. An object of the present invention is to provide a dry non-magnetic toner that can be expected to have an extremely excellent effect on in-machine scattering and a developing device using the dry non-magnetic toner.

  The inventors focused on the external additive of toner particles of a non-magnetic one-component toner used in a hybrid developing system corresponding to a highly durable system, particularly titanium oxide used as an abrasive. The present invention has been completed by externally adding both low resistance titanium oxide and high resistance titanium oxide surface-treated with the titanate coupling agent to be used to toner particles.

That is, according to the first aspect of the present invention, in the non-magnetic toner for developing an electrostatic latent image, the non-magnetic toner has an external additive on the surface of toner particles composed of at least a binder resin and a pigment.
The external additive is formed by externally adding both low resistance titanium oxide and high resistance titanium oxide surface-treated with a titanate coupling agent to toner particles, and the volume resistivity value of the low resistance titanium oxide is: 10 ¹ to 10 ⁶ Ω · cm, and the high resistivity titanium oxide has a volume resistivity of 10 ⁸ to 10 ¹³ Ω · cm. Both resistance values satisfy the following equation: It is set as follows.
In (high resistance titanium oxide resistance value) -In (low resistance titanium oxide resistance value)> 2

In this case, in the non-magnetic toner, the amount added to the toner is 0.6, which is the total value of low resistance titanium oxide and high resistance titanium oxide surface-treated with a titanate coupling agent. It is preferable that the low resistance titanium oxide is added in the range of up to 2.0% by weight and the low resistance titanium oxide is equal to or more than the high resistance titanium oxide. Preferably, in the non-magnetic toner, the addition amount to the toner is On the other hand, low resistance titanium oxide surface-treated with a titanate coupling agent is added in the range of 0.3 to 1.0% by weight and high resistance titanium oxide in the range of 0.3 to 1.0% by weight, respectively. Preferably, the total value of low-resistance titanium oxide and high-resistance titanium oxide is within the range of 0.6 to 1.5% by weight, and the low-resistance titanium oxide is 0.3 to 1. 0% by weight and high resistance titanium oxide is 0.3 ~ It is preferable are respectively added in the range of .5 weight percent.
In addition, when the non-magnetic toner for developing an electrostatic latent image has a magnetic roller at the center of the coordinate axis, it is particularly effective when used in a developing device in which the developing roller is positioned on the lower side in the gravity direction in the rotating direction of the magnetic roller.

According to a second aspect of the present invention, there is provided a magnetic roller for holding a two-component developer composed of the non-magnetic toner and a carrier, and a toner layer formed on the developing roller from the developer held on the magnetic roller to form a toner layer and the photosensitive roller. In the developing device that performs development with a gap between the toner and the body, the non-magnetic toner has an external additive on the surface of toner particles composed of at least a binder resin and a pigment, and the external additive is a titanate cup. Both low resistance titanium oxide and high resistance titanium oxide surface-treated with a ring agent are externally added to toner particles, and the volume resistivity of the low resistance titanium oxide is 10 ¹ to 10 ⁶ Ω · cm. And a non-magnetic toner having a volume resistivity value of high resistance titanium oxide in the range of 10 ⁸ to 10 ¹³ Ω · cm. Is the current Device, when placed in the axes around the magnetic roller, and wherein the developing roller to the magnetic roller rotation direction is developing device located under the direction of gravity.

  In the present invention, since both low-resistance titanium oxide and high-resistance titanium oxide are externally added to the toner particles, toner charge-up during printing durability is reduced, and toner adhesion to the developing roller 4 is prevented while charging. An extremely excellent effect can be expected for scattering in the toner machine due to a decrease in the amount.

  Specifically, the toner of the present invention has low resistance by externally treating both low resistance titanium oxide and high resistance titanium oxide surface-treated with a titanate coupling agent as external additives. The present invention is effectively achieved by separating the functions of titanium oxide and high-resistance titanium oxide. Low-resistance titanium oxide is added as a measure against sleeve adhesion and image density reduction due to toner charge-up during printing durability. On the other hand, high resistance titanium oxide is added because low-resistance titanium oxide alone causes poor charging during printing durability and is likely to cause scattering in the toner machine.

In this case, the volume resistivity of the low resistance titanium oxide surface-treated with the titanate coupling agent is in the range of 10 ¹ to 10 ⁶ Ω · cm, and the volume resistivity of the high resistance titanium oxide is It sets so that it may exist in the range of 10 < ⁸ > -10 < ¹³ > (omega | ohm) * cm.
However, if the low resistance titanium oxide is less than 10 ¹ Ω · cm, it becomes impossible to impart sufficient positive chargeability to the toner, which causes scattering in the toner machine. On the other hand, if it exceeds 10 ⁶ Ω · cm, the charge amount is too high, and the durability is also charged up, resulting in sleeve adhesion, image density reduction, and durability deterioration.
In addition, if the high resistance titanium oxide is less than 10 ⁸ Ω · cm, the role of the high resistance titanium oxide that imparts proper charge is insufficient, and image defects such as a decrease in image density are caused. If it exceeds 10 ¹³ Ω · cm, the charge amount is too high, and the durability is also charged up, resulting in sleeve adhesion, image density reduction, and durability deterioration.
If the difference in resistance between the high resistance titanium oxide and the low resistance titanium oxide is small, the effect of charging stability cannot be exhibited.
Therefore, both resistance values must be set so as to satisfy the following expression.
In (high resistance titanium oxide resistance value) -In (low resistance titanium oxide resistance value)> 2
The volume resistivity value of the titanium oxide can be obtained at an applied voltage of DC 10 V by applying a load of 1 kg using an R8340A ULTRA HIGH RESISTANCE METER manufactured by ADVANTEST.

Further, in the present invention, the amount of titanium oxide surface-treated with a titanate coupling agent in the toner is such that the low-resistance titanium oxide surface-treated with a titanate coupling agent and high resistance are added to the toner. It is preferable that the total value of titanium oxide is within the range of 0.6 to 2.0% by weight, and the low resistance titanium oxide is preferably added more or less than the high resistance titanium oxide, more specifically. The low resistance titanium oxide surface-treated with a titanate coupling agent is added in the range of 0.3 to 1.0% by weight and high resistance titanium oxide in the range of 0.3 to 1.0% by weight, respectively. It is good to be.
When the total value of the low resistance titanium oxide and the high resistance titanium oxide is less than 0.6% by weight, the polishing is insufficient, causing filming on the surface of the photoreceptor and occurrence of image flow at high temperature and high humidity. If the total value of low resistance titanium oxide and high resistance titanium oxide is 2.0% by weight or more, the polishing force on the drum surface becomes too strong and the life of the drum is shortened.
Further, if the low resistance titanium oxide is less than 0.3, it tends to cause a decrease in image density at the time of printing, and if the low resistance titanium oxide exceeds 1.0% by weight, it is difficult to impart proper charge.
On the other hand, if the high resistance titanium oxide is less than 0.3% by weight, the role of the high resistance titanium oxide for imparting proper charging becomes insufficient, and image defects such as a decrease in image density are caused.
When the high resistance titanium oxide exceeds 1.0% by weight, the role of the low resistance titanium oxide is lowered.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  FIG. 1 is a schematic view of an embodiment of a developing device that performs the developing method in the image forming apparatus according to the present invention, and FIG. 2 is a schematic view of an embodiment of the image forming apparatus having the developing device according to the present invention.

  In FIG. 1, reference numeral 1 denotes a photosensitive member (latent image carrier) drum, 2 denotes an exposure device using an LED or the like, 3 denotes a charger for charging the photosensitive drum 1, 4 denotes a developing roller, and 5 denotes an inside. A magnetic roller composed of a rotating sleeve having a magnetic assembly formed on the surface and carrying a magnetic brush composed of carrier and toner on its surface, and 7 a regulation for regulating the thickness of the magnetic brush on the magnetic roller 5 The blades 8a and 8b mix the toner supplied from the toner container 9 with the carrier and stir and stir and charge the mixer, 11 is the recording paper, 12 is the recording paper, 12 is the developing device, and 15 is the alternating current with the developing roller 4. An AC power source for applying a bias, 16 is a DC power source for applying a DC bias, and 17 is a DC power source for applying a DC bias to the magnetic roller 5.

  In FIG. 2, 20 is an image forming apparatus, 53 is a paper feed cassette, 54 is an endless belt, 58 is a transfer device, and 59 is a fixing device. In the following description, a case where the present invention is applied to a tandem type page printer will be described as an example, and a case where the photosensitive drum 1 is used as a photosensitive member will be described as an example. Needless to say, the present invention may be applied to other types of color image forming apparatuses, and the photosensitive member may be a belt-shaped photosensitive belt.

The developing device 12 is a vertical developing device because the positional relationship between the magnetic roller 5 and the nearest mixer 8a is the upper portion of the mixer 8a, and the photosensitive member 1 and the exposure device are placed under the mixer 8a and the mixer 8b. Since the two developing devices 12 are arranged as shown in FIG. 2, the depth of the image forming device 20 can be reduced. Further, the toner container 9 can be freely dropped from the toner replenishing port via a motor by disposing it at the upper part of the developing device 12, and at the time of replacement, it can be removed from the top and mounted again from above. Similarly to the toner container 9, it can be removed at the top, and it is easy to remove even when the developing device 12 is abnormal, and the structure is simplified.
The developing device is arranged so that the developing roller is positioned on the lower side in the direction of gravity when the magnetic roller 5 is centered on the coordinate axis.

  First, the operation of an embodiment of the image forming apparatus 20 to which the developing method by the developing device 12 configured as described above is applied will be described with reference to the schematic diagram of FIG. In the image forming apparatus 20, an endless belt 54 is disposed so as to be able to convey the recording paper from the paper feed cassette 53 toward the fixing device 59, and a black belt is disposed above the belt 54 that conveys the recording paper. Developing device 12A, yellow developing device 12B, cyan developing device 12C, and magenta developing device 12D. In these developing devices 12 (A, B, C, D), the magnetic roller 5 (A, B, C, D) and the magnetic roller 5 (A, B, C, D) are respectively developed in close proximity. A roller 4 (A, B, C, D) is disposed, and the photosensitive drum 1 (A, B, C, D) faces the developing roller 4. Further, around the photosensitive drum 1, A charger 3 (A, B, C, D) and an exposure device 2 (A, B, C, D) are arranged.

  In the tandem type page printer configured as described above, the two-component developer including toner and carrier corresponding to each color such as yellow, cyan, magenta, and black is supplied from the toner container 9 to each developing device 12. The magnetic brush 10 is formed on the magnetic roller 5 by being stirred and charged by the mixers 8a and 8b shown in FIG. The magnetic brush 10 on the magnetic roller 5 is layer-regulated by the regulating blade 7 and developed by the potential difference between the DC bias 17 applied to the magnetic roller 5 and the DC bias 16 applied to the developing roller 4 and the AC bias 15. A thin layer of toner only is formed on the roller 4.

  When a print start signal is received from a control circuit (not shown), first, the photosensitive drum 1 composed of a positively charged organic photoreceptor (positive OPC) is charged by the charger 3 to 400 V, for example, and then, for example, 770 nm. As a result of exposure by the exposure apparatus 2 using LEDs having a wavelength of, the post-exposure potential of the photosensitive drum 1 becomes about 70 V, and a latent image is formed. The latent image is developed with the toner flying from the toner thin layer on the developing roller 4 to the photosensitive drum 1 by a DC bias 16 and an AC bias 15 applied to the developing roller 4 to form a toner image. When the recording paper is fed from the paper feed cassette 53 and sent by the belt 54 to reach the photosensitive drum 1, a transfer bias by the transfer device 58 (A, B, C, D) is applied to the recording paper. The toner image is transferred to the toner image, fixed by the fixing device 59, and discharged. Thereafter, as described above, the thin toner layer on the developing roller 4 is collected on the magnetic roller 5 by changing the direct current (DC) bias 17 while applying the alternating current (AC) bias 15 periodically according to the print data.

  In such an image forming apparatus, when a positively charged organic photosensitive member (positive OPC) is used as the photosensitive material for the photosensitive member 1, the generation of ozone and the like is small, and charging is stable. Even when the film thickness is changed over a long period of time, the change in the photosensitive characteristics is small and the image quality is stable.

That is, when a long-life system is used, the film thickness of the positive OPC photoreceptor is set to about 20 μm to 40 μm. In the case of 20 μm or less, when the film decreases and reaches 10 μm, black spots are noticeably generated due to dielectric breakdown. On the other hand, if the film thickness is thicker than 40 μm, the sensitivity is lowered and the image is lowered.
The exposure apparatus 2 may be a system using a semiconductor laser or LED. A wavelength near 770 nm is effective for positive OPC, and a wavelength near 685 nm is effective for an a-Si photoreceptor. Hereinafter, an example in which a positive OPC photoreceptor is used will be described.

The positive OPC photosensitive member, which is an electrostatic latent image carrier, is charged to 400 V by the charger 3. Thereafter, when exposure is performed with an LED having a wavelength of 770 nm, the post-exposure potential is set to 70V. The positive OPC photosensitive member is disposed with a space of about 250 μm with respect to the developing roller 4. No wire electrode or the like is used in this space. The surface of the developing roller 4 is a rotating body made of conductive aluminum. The material of the sleeve may be a uniform conductor, and SUS, conductive resin coating, etc. can be applied. A thin toner layer is formed on the developing roller 4 by the potential difference between the developing roller 4 and the magnetic roller 5. As for the potential difference, the toner layer pressure of about 1 to 1.5 mg / cm ² is formed on the developing roller 4 by setting the potential of the developing roller to 70V and the potential of the magnetic roller to 400V. At this time, an appropriate charge amount of the developer is about 10 to 20 μC / g. When the amount is 10 μC / g or less, toner scattering is conspicuous, and when the amount is 20 μC / g or more, the toner formed in a thin layer is difficult to fly to the photoreceptor 1. . In order to cause the toner to fly from the developing roller 4 to the photoreceptor 1, developability is obtained by applying an AC voltage to the developing roller. As the voltage, P−P = 1.5 KV, f = 3.0 Hz, and the balance of image density, dot reproduction, and fog removal was balanced. Further, the development ghost could be removed by setting the DUTY ratio to 30%.
When the potential across the toner layer surface of the developing roller 4 is measured, it is about 320 V, and it can be said that 320 V-70 V (photoreceptor potential after full exposure) = 250 V is the actual execution potential.

The gap between the magnetic roller 5 and the developing roller 4 is set to 400 μm, and the gap between the regulating blade 7 and the magnetic roller 5 is adjusted according to the particle size of the carrier. The developer is set to 400 to 500 μm, and the magnetic brush is in contact with the developing roller 4. If the gap between the developing roller 4 and the magnetic roller 5 is too wide, the developer cannot pass between the rollers and overflows. If it is too narrow, the developer cannot contact the developing roller and it becomes difficult to collect the toner on the developing roller. When the operation is repeated, the toner gradually adheres to the developing roller 4 and the toner cannot fly to the photoreceptor 1.
The magnetic roller 5 and the restricting blade 7 run the magnetic lines of force, thereby reducing the transportability of the magnetic brush, and increasing the transport force of the surface of the magnetic roller 5 by knurling or blasting to prevent the restriction blade 7 and the magnetic roller 5 from moving. The gap margin can be relaxed.

Further, since the positional relationship between the magnetic roller 5 and the nearest mixer 8a is the upper part of the mixer, a vertical developing device is formed. By arranging four developing devices, the depth of the printer main body can be reduced. This is because the next photosensitive member and the exposure apparatus can be placed under the mixer 8a and the mixer 8b. Further, the toner container 9 can be freely dropped from the toner replenishing port via a motor by being disposed at the top of the developing device, and has a simple structure in which it can be removed from the top and replaced from the top at the time of replacement. It becomes possible.
As with the toner container 9, the developing device can be removed at the top, and can be easily removed when the developing device is abnormal, and the structure is simplified.

Next, the toner used in the developing device is obtained by dispersing various toner compounding agents such as a colorant in a binder resin. The type of binder resin used for the toner in the present embodiment is not particularly limited. For example, styrene resin, acrylic resin, styrene-acrylic copolymer, polyethylene resin, polypropylene resin, vinyl chloride. It is preferable to use a thermoplastic resin such as a resin, a polyester resin, a polyamide resin, a polyurethane resin, a polyvinyl alcohol resin, a vinyl ether resin, an N-vinyl resin, or a styrene-butadiene resin.
More specifically, the polystyrene resin may be a homopolymer of styrene or a copolymer with another copolymerizable monomer copolymerizable with styrene. Moreover, as the polyester resin, any resin obtained by condensation polymerization or co-condensation polymerization of an alcohol component and a carboxylic acid component can be used. Moreover, it is preferable that the softening point of a polyester-type resin is 80-150 degreeC, More preferably, it is 90-140 degreeC.
The binder resin may be a thermosetting resin. By introducing a partially crosslinked structure in this way, it is possible to further improve the storage stability, form retention, and durability of the toner without deteriorating the fixability. Therefore, it is not necessary to use 100 parts by mass of the thermoplastic resin as the binder resin of the toner, and it is also preferable to add a crosslinking agent or to partially use a thermosetting resin.

Therefore, an epoxy resin, a cyanate resin, or the like can be used as the thermosetting resin. Moreover, in this invention, it is preferable that the glass transition point (Tg) of binder resin is 55-70 degreeC, More preferably, it is 55-65 degreeC. When the glass transition point is lower than the above range, the obtained toners are fused with each other in the developing device, and the storage stability is lowered. Further, since the resin strength is low, there is a tendency that toner adheres to the photoreceptor. Further, when the glass transition point is higher than the above range, the low-temperature fixability of the toner is lowered. In addition, the glass transition point of binder resin can be calculated | required from the change point of specific heat using a differential scanning calorimeter (DSC). More specifically, it was obtained by measuring an endothermic curve using a differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc. as a measuring device. 10 mg of a measurement sample was put in an aluminum pan, an empty aluminum pan was used as a reference, a measurement temperature range of 25 to 200 ° C., and a temperature increase rate of 10 ° C./min. The glass transition point was obtained from the obtained endothermic curve.
The colorant is not particularly limited, and examples thereof include black, magenta, cyan and yellow pigments. These colorants are usually blended in an amount of 2 to 20 parts by mass, preferably 5 to 15 parts by mass with respect to 100 parts by mass of the binder resin.
Charge control agents are blended to remarkably improve the charge level and charge rise characteristics (an indicator of whether to charge to a constant charge level in a short time), and to obtain characteristics such as durability and stability. It is. That is, when the toner is positively charged for development, a positively chargeable charge control agent is added. When the toner is negatively charged for development, a negatively chargeable charge control agent can be added. .
Such a charge control agent is not particularly limited, but in particular, the nigrosine compound is most suitable for use as a positively chargeable toner from the viewpoint of obtaining a quicker rising property. A styrene-acrylic copolymer resin having a quaternary ammonium salt as a functional group is optimal from the viewpoint that the charge amount can be easily adjusted to a value within a desired range.
As the charge control agent exhibiting negative chargeability, for example, organometallic complexes and chelate compounds are effective, and acetylacetone metal complexes, salicylic acid-based metal complexes or salts are particularly preferable, and salicylic acid-based metal complexes or salicylic acid-based metal salts are particularly preferable.
The waxes used for improving the fixing property and the offset property are not particularly limited.

  The toner is prepared by mixing the above-described binder resin and various toner compounding agents such as a charge control agent, melt-kneading using a kneader such as an extruder, and then cooling, pulverizing and classifying the toner. can get. The above toner is generally preferably classified and adjusted in particle size so that the average particle size is about 5 to 15 μm. Further, the toner particle surface can be treated with colloidal silica, hydrophobic silica or the like for the purpose of maintaining the fluidity and storage stability of the toner.

  In addition, the silica fine particles and titanium oxide are externally added by dry mixing with the toner. This stirring and mixing is performed so that the fine particles are not embedded in the toner, such as a Henschel mixer or a Nauter mixer. It is better to use.

As the carrier used in the developing device, magnetite carrier, Mn-based ferrite, Mn-Mg-based ferrite, etc. can be used. These carriers may be used as they are, but the surface does not increase the appropriate resistance value. It is also possible to process and use. In the present invention, as an example, a ferrite carrier having a volume resistivity of 10 ⁸ Ωcm ³ and a saturation magnetization of 40 emu / g and an average particle size of 35 μm was used. If the average particle size exceeds 50 μm, the carrier stress increases and the toner density cannot be increased, and the amount of toner supplied to the developing roller 4 decreases.

Hereinafter, the toner for performing the experiment of the present invention will be described based on examples. Needless to say, the following description exemplifies the present invention, and the scope of the present invention is not limited to the following description without any particular reason.
First, a method for adjusting the volume resistivity value of the titanium oxide will be described.
A colloidal titanium compound obtained by neutralizing and precipitating a titanium tetrachloride solution with sodium hydroxide was aged, calcined at 575 ° C., and pulverized with a hammer mill to obtain titanium dioxide having an average particle diameter of 0.25 μm. This titanium dioxide was dispersed in water, sodium pyrophosphate was further added, and wet grinding was performed with a sand mill to obtain a water-soluble slurry having a titanium dioxide concentration of 50 g / l.
After the slurry was heated to 80 ° C., a solution prepared by dissolving appropriate amounts of tin chloride (SnCl ₄ -5H ₂ O) and antimony chloride (SbCl ₃ ) in 300 cc of 2N hydrochloric acid solution, 10% sodium hydroxide solution, Was added over 60 minutes while maintaining the pH at 6-9 to form a coating layer composed of tin oxide and antimony oxide on the surface of the titanium dioxide particles.

In this case, the amount is decreased when the resistance value is increased, and the amount is increased when the resistance value is decreased. Further, the resistance value can be lowered by increasing the ratio of antimony chloride by the ratio of tin chloride and antimony chloride.
Thereafter, the pH of the slurry was finally adjusted to 8, and then filtered and washed until the specific resistance of the filtrate reached 20,000 Ω · cm, and dried (120 ° C.).
The titanium dioxide dried material thus obtained was calcined in an electric furnace at 500 ° C. for 60 minutes, and then crushed with a jet mill, and the volume resistivity values shown in Examples 1 to 7 and Comparative Examples 1 to 6 were obtained. The obtained low resistance titanium oxide and high resistance titanium oxide were obtained.
Furthermore, the final desired titanium oxide was obtained by surface-treating the obtained titanium oxide with a titanate coupling agent.

Next, the toners shown in the present example and the comparative example are prepared by the low resistance titanium oxide and the high resistance titanium oxide having the volume specific resistance values shown in the above Examples 1 to 7 and Comparative Examples 1 to 6.
First, 100 parts by mass of a binder resin, 6 parts by mass of a wax as a release agent (Sazol Wax H1, manufactured by Sasol), and a quaternary ammonium salt (Bontron P-51, manufactured by Orient Chemical) as a positive charge control agent 6 parts by mass and 4 parts of carbon black (product number: MA100 company name: Mitsubishi Chemical) as a pigment were mixed with a Henschel mixer, melted and kneaded with a twin screw extruder, cooled, and ground with a hammer mill. . Further finely pulverized by a mechanical pulverizer was classified by an airflow classifier to obtain a toner having a volume average particle size of 9.0 μm.
To the toner powder (non-magnetic one-component toner) obtained above, 1.0 part by mass of silica (RA-200H: manufactured by Nippon Aerosil Co., Ltd.), specific volume according to Examples 1-7 and Comparative Examples 1-6 Examples 1 to 7 and Comparative Examples in which mass parts shown in Table 1 below are added to low resistance titanium oxide and high resistance titanium oxide showing resistance values, externally added by a Henschel mixer, and adhered to the surface of the toner powder. Nonmagnetic positively charged toners 1 to 6 were prepared.

Next, the hand charging characteristics of the toners shown in Examples 1 to 7 and Comparative Examples 1 to 6 were measured as follows.
4 parts by mass of the nonmagnetic positively charged toner shown in Examples 1 to 7 and Comparative Examples 1 to 6 and 100 parts by mass of a ferrite carrier (FK-150, manufactured by Powdertech) are mixed for 30 minutes in a normal environment. The charge amount (μC / g) when frictionally charged was defined as the initial charge amount.
That is, after mixing in a normal temperature and normal humidity environment, it is triboelectrically charged by stirring for 60 minutes in a ball mill. Of these, a charge amount of about 100 mg was measured using a charge amount measuring device (Q / M Meter 210HS) manufactured by TREK, and the charge amount μC / g per gram of the developer was determined from the mass change at that time.
Details of the measurement are as shown in Table 2 below.

Next, image characteristics are examined using the tandem page printer shown in FIGS.
In the normal temperature and humidity environment (20 ° C, 65% RH), an image evaluation pattern is printed by the page printer at the initial stage to make an initial image, and then 100,000 sheets are continuously fed, and the image evaluation pattern is printed again. Each of the solid images was measured using a Macbeth reflection densitometer (RD914). The image density was 1.30 or higher.

In the measurement of scattering in the toner machine, 100,000 sheets were continuously passed, an image evaluation pattern was printed again, and the scattering in the toner machine was confirmed implicitly.
○: No toner dropped from the developer. There is no LED contamination.
X: Toner is dropped. Or there is LED contamination and it appears in the image.

The surface state of the photosensitive member was continuously passed 100,000 sheets, and the surface of the drum was visually observed and the image was confirmed to judge the state of the drum.
○: No drum adhesion on drum surface and image.
X: Drum adheres. The drum tube is exposed due to film reduction.

In addition, 100,000 sheets were continuously fed in the state of the developing roller 4, and toner adhesion to the developing roller 4 was confirmed by visual observation.
○: No toner adheres to the sleeve and there is no decrease in image density.
X: Toner sleeve adhesion is visually observed, causing a decrease in image density.

The experimental results based on the measurement will be described in detail below.
About Examples 1-7, the sleeve adhesion, image density, in-machine scattering, and the state of the photoreceptor were good by using low resistance titanium oxide and high resistance titanium oxide in combination.
In Comparative Example 1, only low-resistance titanium oxide is externally added, but the initial charge amount tends to be lower than the other ones. The evaluation was stopped midway.
In Comparative Example 2, only high resistance titanium oxide was externally added, but there was no problem with the charge amount and image density in the initial stage, but the charge amount increased with continuous printing and sleeve adhesion occurred. As a result, the image density was lowered.
Comparative Example 3 was a combination of low resistance titanium oxide and high resistance titanium oxide. However, since the addition amount was as small as 0.3%, the polishing power was insufficient and drum filming occurred.
Comparative Example 4 is a combination of low-resistance titanium oxide and high-resistance titanium oxide. However, since the addition amount was as large as 4%, the polishing force was too strong, the film thickness of the drum was severe, and the photosensitive layer was less than 10 μm. Appeared and leaked at that part, resulting in a defective image.
In Comparative Example 5, two types of high-resistance titanium oxides were used in combination, but at the time of printing, the toner was charged up and sleeve adhesion occurred, resulting in a decrease in image density.
In Comparative Example 6, since the difference in resistance value between the high resistance titanium oxide and the low resistance titanium oxide was small, the effect of charging stability could not be exhibited, and sleeve adhesion occurred.
Therefore, it was confirmed that both resistance values must satisfy the following formula.
In (high resistance titanium oxide resistance value) -In (low resistance titanium oxide resistance value)> 2

As is apparent from the above description, according to the first aspect of the present invention, since both low resistance titanium oxide and high resistance titanium oxide are externally added to the toner particles, toner charge-up during printing durability is reduced. While preventing the toner from adhering to the developing roller, it is possible to expect an extremely excellent effect against scattering in the toner machine due to a decrease in the charge amount.
In particular, according to a second aspect of the present invention, in a so-called hybrid development system using non-magnetic toner, toner charge-up at the time of printing durability is reduced, toner adhesion to the developing roller is prevented, and scattering in the toner machine due to a decrease in charge amount is also achieved. In contrast, an extremely excellent developing device can be obtained.

1 is a schematic diagram of an embodiment of a developing device that performs a developing method in an image forming apparatus according to the present invention. 1 is a schematic diagram of an embodiment of an image forming apparatus having a developing device according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive body (latent image carrier) drum 2 Exposure apparatus 3 Charger 4 Developing roller 5 Supply roller (magnetic roller)
7 Regulating blade 8a, 8b Mixer 9 Toner container 10 Magnetic brush 11 Recording paper 12 Developing device 15 AC power source 16 DC power source 17 DC power source

Claims (5)

In the non-magnetic toner for developing an electrostatic latent image having an external additive on the surface of toner particles made of a binder resin and a pigment,
The external additive is formed by externally adding both low resistance titanium oxide and high resistance titanium oxide surface-treated with a titanate coupling agent to toner particles, and the volume resistivity value of the low resistance titanium oxide is: 10 ¹ to 10 ⁶ Ω · cm, and the high resistivity titanium oxide has a volume resistivity of 10 ⁸ to 10 ¹³ Ω · cm. Both resistance values satisfy the following equation: Further, the addition amount of titanium oxide to the non-magnetic toner is 0 to the total value of low resistance titanium oxide and high resistance titanium oxide surface-treated with a titanate coupling agent. A nonmagnetic toner for developing an electrostatic latent image, wherein the non-magnetic toner is within a range of from 6 to 2.0% by weight and the low-resistance titanium oxide is added to the same amount or more than the high-resistance titanium oxide.
In (high resistance titanium oxide resistance value) -In (low resistance titanium oxide resistance value)> 2   The amount of titanium oxide added to the non-magnetic toner is 0.3 to 1.0% by weight of low resistance titanium oxide surface-treated with a titanate coupling agent, and high resistance titanium oxide is added to the toner. The nonmagnetic toner for developing an electrostatic latent image according to claim 1, wherein the nonmagnetic toner is added within a range of 0.3 to 1.0% by weight.   The total value of the low resistance titanium oxide and the high resistance titanium oxide is within the range of 0.6 to 1.5% by weight, and the low resistance titanium oxide is 0.3 to 1.0% by weight. The nonmagnetic toner for developing electrostatic latent images according to claim 1, wherein the nonmagnetic toner is added within a range of 0.3 to 0.5 wt%. A magnetic roller for holding a two-component developer composed of a non-magnetic toner and a carrier, and a thin toner layer is formed on the developing roller from the developer held on the magnetic roller, and a gap is formed between the developing roller and the photosensitive member. The non-magnetic toner has an external additive on the surface of toner particles composed of at least a binder resin and a pigment, and the external additive is surface-treated with a titanate coupling agent. Both low resistance titanium oxide and high resistance titanium oxide are externally added to toner particles, and the volume resistivity value of the low resistance titanium oxide is in the range of 10 ¹ to 10 ⁶ Ω · cm, A developing apparatus using a non-magnetic toner having a volume resistivity value of high resistance titanium oxide in a range of 10 ⁸ to 10 ¹³ Ω · cm.   5. The developing device according to claim 4, wherein the developing device is a developing device in which the developing roller is positioned on the lower side in the direction of gravity when the magnetic roller is centered on the coordinate axis.

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