JP2005346102A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device and an image forming apparatus which have less changes in the bulk density of a developer and with which the toner concentration can be stably controlled even when the developer is used with intense stress given to the developer. <P>SOLUTION: The developing device is equipped with: a developer 28M comprising toner comprising at least a binder resin and a pigment, and a carrier having a coating layer containing at least a binder resin and particles; a toner concentration detecting means to detect the toner concentration of the developer 28M; and a controlling means to control the toner concentration on the basis of the detection result of the toner concentration detecting means. A bulk density sensor 26M is used for the toner concentration detecting means. The particle diameter (D) of the particles and the film thickness (h) of the binder resin are controlled to satisfy the relation of 1<[D/h]<10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, and more specifically, a carrier having a coating film having at least a binder resin and a pigment, and at least a binder resin and particles. A developing device and an image forming apparatus comprising: a developer comprising: a toner density detecting unit that detects a toner density of the developer; and a control unit that controls the toner density based on a detection result of the toner density detecting unit. It is about.

  In general, in image forming methods such as electrophotography and electrostatic photography, a developer obtained by stirring and mixing a toner and a carrier in order to develop an electrostatic latent image formed on a latent image carrier. Is used. This developer is required to be a suitably charged mixture. In general, as a method for developing an electrostatic latent image, a method using a two-component developer obtained by mixing a toner and a carrier and a method using a one-component developer containing no carrier are known. . The former developing method using a two-component developer can provide a relatively stable and good image, but has a drawback that carrier deterioration and fluctuation in the mixing ratio of the toner and the carrier are likely to occur. On the other hand, the latter one-component developer does not have the disadvantages of the former, but has the disadvantage that the chargeability is difficult to stabilize.

  Also, when developing electrostatic latent images repeatedly using a two-component developer, the toner in the developer is consumed and the toner density fluctuates, so it is necessary to obtain a stable image during printing. Therefore, it is necessary to replenish the toner and suppress this fluctuation. In general, as a method for controlling the toner replenishment amount, an image forming apparatus such as a copying machine includes a permeability detection sensor, a fluidity detection sensor, an image density detection sensor, a bulk density detection sensor, and the like. Among these sensors, an image density detection sensor, or a combination of an image density detection sensor and a magnetic permeability sensor (a kind of bulk density sensor) is used recently. The toner density control by the image density detection sensor is a method of controlling the toner replenishment amount by developing a constant image pattern on the latent image carrier and detecting the image density from reflected light. Further, toner density control using a combination of an image density detection sensor and a magnetic permeability sensor is a method of controlling the amount of toner replenishment by changing the target value of the magnetic permeability sensor according to the density of the image pattern.

  The granular carrier used in such a two-component development system is capable of preventing toner filming on the carrier surface, forming a uniform carrier surface, preventing surface oxidation, preventing moisture sensitivity deterioration, extending the life of the developer, and photosensitive. For the purpose of protecting the body from scratches or abrasion by the carrier, controlling the polarity of the charge, or adjusting the amount of charge, a hard and high-strength coating layer is usually provided by coating with an appropriate resin material. For example, those coated with a specific resin material (Japanese Patent Laid-Open No. 58-108548), and various additives added to the coating layer (Japanese Patent Laid-Open No. 54-1555048, Japanese Patent Laid-Open No. 57) -40267, JP-A-58-108549, JP-A-59-166968, JP-B-1-19584, JP-B-3-628, JP-A-6-202. 81), further using an additive added to the carrier surface (Japanese Patent Laid-Open No. 5-273789), and using a coating film containing conductive particles larger than the coating film thickness. (Japanese Patent Laid-Open No. 9-160304) and the like are disclosed. JP-A-8-6307 discloses that a benzoguanamine-n-butyl alcohol-formaldehyde copolymer is used as a main component for a carrier coating material, and Japanese Patent No. 2683624 discloses a melamine resin and an acrylic resin. Is used as a carrier coating material.

  However, even when a coating layer is provided on the carrier, the toner and the carrier are used when a low image area original (especially an image area of 3% or less) with a high stress on the developer is used like a continuous run. The carrier is charged up due to the frictional charging, and a phenomenon in which the bulk density of the developer decreases (the volume increases) due to the repulsive force between the carriers may occur. This phenomenon is further accelerated when the external additive of the toner is embedded by rubbing between the carriers and the fluidity of the entire developer is lowered. The output of the magnetic permeability sensor decreases as the carrier, which is a magnetic material, is farther away or as the carrier is sparser. Therefore, if the carrier is separated from the upper part of the sensor due to the decrease in the developer bulk density, the toner density does not change, but the output is lowered and the toner density is increased. End up. For this reason, the developing ability is reduced due to a decrease in toner density based on the detection result. As described above, when the developer is used in such a way that a high stress is applied, there is a problem that toner density control becomes unstable due to a change in the bulk density of the developer.

  In the inventions disclosed in Japanese Patent Application Laid-Open Nos. 11-316495 and 10-186833, toner density control is not possible due to fluctuations in the bulk density of the developer when the image forming apparatus is paused for a long time. It solves the problem of becoming stable. However, in the inventions disclosed in these publications, there is no problem with toner density control becoming unstable due to fluctuations in the bulk density of the developer when the developer is subjected to high stress. Not mentioned.

  The present invention has been made in view of the above circumstances, and the purpose of the present invention is to reduce the bulk density fluctuation of the developer and to stabilize it even when the developer is used in such a way that high stress is applied. It is an object of the present invention to provide a developing device and an image forming apparatus that can perform toner density control.

In order to achieve the above object, the invention of claim 1 provides a developer comprising at least a toner comprising a binder resin and a pigment, a carrier having a coat film having at least a binder resin and particles, In a developing device comprising a toner density detecting means for detecting a toner density and a control means for controlling the toner density based on a detection result of the toner density detecting means, a bulk density sensor is used as the toner density detecting means, and The particle diameter (D) of the particles and the film thickness (h) of the binder resin satisfy the relationship 1 <[D / h] <10. When the present inventors conducted earnest experiments, in a carrier having a coating film having at least a binder resin and particles, the particle diameter (D) and the film thickness (h) of the binder resin are 1 <[D / h] <10, and more desirably 1 <[D / h] <5, so that the developer can suppress the bulk density fluctuation of the developer even when the developer is subjected to high stress. It was found that it was obtained remarkably. This is presumably because the particles are more convex than the coat film, so that the contact area between the carriers during stirring is reduced, and the charge up of the carriers can be reduced. Further, it is considered that since the space between the carriers is created by the unevenness of the particles (spacer effect), the degree of rubbing the toner during stirring is reduced, and the embedding of the external additive of the toner can also be reduced. For these reasons, if the toner concentration is constant, a decrease in the bulk density (increase in the bulk) of the developer is suppressed, and the fluctuation of the bulk density can be reduced. In this way, since the bulk density variation is small except for the toner density change, erroneous detection of the bulk density sensor can be prevented, and stable toner density control can be performed. In addition, when [D / h] is 1 or less, the particles are buried in the binder resin. On the other hand, when [D / h] is 10 or more, since the contact area between the particles and the binder resin is small, a sufficient restraining force cannot be obtained, and the particles are easily detached. In order to prevent the particles from detaching, it is more preferable that [D / h] is 5 or less. In JP 2001-188388 A, in a carrier having a coating film having at least a binder resin and particles, the particle diameter (D) and the binder resin film thickness (h) are 1 <[D / h. An electrophotographic carrier characterized in that <5 is disclosed. This publication does not mention the problem of the present invention that the toner density is poorly controlled due to the bulk density fluctuation generated as a result of high stress applied to the developer.
In order to achieve the above object, the invention of claim 6 is directed to an image carrier, latent image forming means for forming a latent image on the image carrier, and a latent image formed on the image carrier. And a developing unit that develops the toner using a two-component developer containing a toner and a carrier, the developing device according to claim 1, 2, 3, 4, or 5 is used as the developing unit. It is characterized by the fact that In this image forming apparatus, even when the developer is subjected to high stress, for example, when it is used like a continuous run of a low image area original (particularly, an image area of 3% or less), the bulk density of the developer varies. Stable toner density control can be performed while suppressing the above, and a high-quality image can be formed.

According to the first aspect of the present invention, since the change in the bulk density of the developer can be suppressed even when the developer is subjected to a high stress, the toner density is controlled in combination with the bulk density sensor. Thus, there is an excellent effect that toner density control can be performed very stably.
Further, in the invention of claim 6, even when the developer is subjected to a high stress, the toner density can be stably controlled by suppressing the fluctuation of the bulk density of the developer. There is an excellent effect that a clear image can be formed.

Hereinafter, an embodiment in which the present invention is applied to an electrophotographic color laser printer (hereinafter referred to as “laser printer”) as an image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of a laser printer according to the present embodiment. This laser printer has four sets of image forming means 1M, 1C, 1Y, 1BK (hereinafter referred to as each image forming unit) for forming images of each color of magenta (M), cyan (C), yellow (Y), and black (BK). The subscripts M, C, Y, and BK of the symbols indicate magenta, cyan, yellow, and black members, respectively, and the moving direction of the transfer paper 100 (see FIG. 2) as a transfer material (see FIG. 2). Arranged in order from the upstream side in the direction of arrow A). Each of the image forming units 1M, 1C, 1Y, and 1BK includes a photoconductor unit having photoconductor drums 11M, 11C, 11Y, and 11BK as image carriers, and a developing unit. The image forming units 1M, 1C, 1Y, and 1BK are arranged so that the rotation axes of the photoconductive drums 11M, 11C, 11Y, and 11BK in each photoconductive unit are parallel to each other and in the transfer paper moving direction. It is set to be arranged at a pitch.

  In addition to the image forming means 1M, 1C, 1Y, and 1BK, the laser printer transfers a transfer material toward the optical writing unit 2, the paper feed cassettes 3 and 4, and a transfer portion that faces each of the photosensitive drums 11. A transfer unit 6 having a transfer belt 60 as a transfer material transport belt for transporting a transfer material, a registration roller 5 comprising a pair of rollers for supplying a transfer paper 100 as a transfer material to the transfer belt 60, a belt fixing type fixing unit 7, A paper discharge tray 8 and a reversing unit 9 are provided. The laser printer also includes a manual feed tray, a toner supply container, a waste toner bottle, a power supply unit, and the like (not shown).

  The optical writing unit 2 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photosensitive drums 11M, 11C, 11Y, and 11BK while scanning the laser beam based on image data. To do.

  Also, the alternate long and short dash line in FIG. 1 indicates the conveyance path of the transfer paper 100. The transfer paper 100 fed from the paper feed cassettes 3 and 4 is transported by transport rollers while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration rollers 5 are provided. The transfer paper 100 is supplied to the transfer belt 60 by the registration roller 5 at a predetermined timing, and is conveyed so as to pass through the transfer portions facing the photoconductive drums 11M, C, Y, and BK. As a result, the toner images on the photosensitive drums 11M, 11C, 11Y, and 11BK formed by the image forming units 1M, 1C, 1Y, and 1BK are sequentially superimposed and transferred onto the transfer paper, and are transferred onto the transfer material. A color image is formed. The transfer paper 100 on which the color image is formed is discharged onto the paper discharge tray 8 after the toner image is fixed by the fixing unit 7.

FIG. 2 is an enlarged view showing a schematic configuration of the magenta image forming means 1M among the image forming means 1M, 1C, 1Y and 1BK. Since the other image forming means 1C, 1Y, and 1BK have the same configuration, their descriptions are omitted.
In FIG. 2, the image forming means 1M includes the photoconductor unit 10M and the developing unit 20M as described above. In addition to the photosensitive drum 11M, the photosensitive unit 10M includes a swingable cleaning blade 13M that cleans the surface of the photosensitive drum, a non-contact type charging roller 15M that uniformly charges the surface of the photosensitive drum, and the like. Yes. In addition, a lubricant application / discharge brush roller 12M having a function of applying a lubricant to the surface of the photosensitive drum and discharging the surface of the photosensitive drum is also provided. The lubricant application and static elimination brush roller 12M has a brush portion made of conductive fiber, and a metal base power source (not shown) for applying a static elimination bias is connected to the cored bar portion.

  In the photoreceptor unit 10M having the above configuration, the surface of the photoreceptor drum 11M is uniformly charged by the charging roller 15M to which a voltage is applied. When the surface of the photosensitive drum 11M is irradiated with the laser beam modulated and deflected by the optical writing unit 2 while being scanned, an electrostatic latent image is formed on the surface of the photosensitive drum 11M. The electrostatic latent image on the photosensitive drum 11M is developed by a developing unit 20M described later to become a magenta toner image. In the transfer portion Pt through which the transfer paper 100 on the transfer belt 60 passes, the toner image on the photosensitive drum 11M is transferred to the transfer paper 100. The surface of the photosensitive drum 11M after the toner image is transferred is coated with a predetermined amount of lubricant by a lubricant application / static discharge brush roller 12M and discharged, and then cleaned by a cleaning blade 13M as photosensitive member cleaning means. It is cleaned and prepared for the next formation of an electrostatic latent image.

  The developing unit 20M uses a two-component developer (hereinafter also simply referred to as “developer”) 28M including a magnetic carrier and negatively charged toner as a developer for developing the electrostatic latent image. . The developing unit 20M includes a developing sleeve 22M made of a non-magnetic material as a developer carrying member disposed so as to be partially exposed from the opening on the photosensitive drum side of the developing case 21M, and the inside of the developing sleeve 22M. A magnetic roller (not shown) as a magnetic field generating means fixedly arranged on the toner, a conveying screw 23M, 24M, a developing doctor 25M, a magnetic permeability sensor 26M for detecting the magnetic permeability of the developer 28M as a toner concentration sensor (T sensor), and a powder A body pump 27M and the like are provided. A developing bias voltage in which an AC voltage AC (AC component) is superimposed on a negative DC voltage DC (DC component) is applied to the developing sleeve 22M by a developing bias power source (not shown) as a developing electric field forming unit, and the developing sleeve 22M is applied. Is biased to a predetermined voltage with respect to the metal substrate layer of the photosensitive drum 11M.

  In FIG. 2, the developer 28M accommodated in the developing case 21M is frictionally charged by being agitated and conveyed by the conveying screws 23M and 24M. A part of the developer 28M is carried on the surface of the developing sleeve 22M, the layer thickness is regulated by the developing doctor 25M, and then conveyed to the developing position facing the photosensitive drum 11M. At the development position, the electrostatic latent image on the photosensitive drum 11M is developed by the charged toner in the developer on the development sleeve 22M.

  Since the toner concentration of the developer 28M in the developing case 21M decreases due to the consumption of the developer accompanying the image formation, a toner cartridge (not used) may be necessary depending on the image area and the detected value (Vt) of the magnetic permeability sensor 26M. The toner is replenished by the powder pump 27M from the figure) and is kept substantially constant. Toner replenishment is based on the difference ΔT (= Vref−Vt) between the toner density target value (Vref) and Vt, and when ΔT is + (plus), the toner density is considered to be sufficiently high and toner is not replenished. .DELTA.T is-(minus), the toner replenishment amount is increased as | .DELTA.T | is larger, so that Vt approaches the value of Vref. Further, process control (for example, a plurality of halftones and solid patterns formed on the photosensitive drum 11M is converted into an adhesion amount by a reflection density sensor once every 10 sheets (about 5 to 200 sheets depending on copy speed, etc.) Vref, charging potential, and light quantity are set according to the target setting). In order to perform such toner density control, a control unit (not shown) is provided, and this control unit includes a CPU, a ROM, a RAM as storage means, an I / O interface, and the like.

  Of the four photosensitive drums 11M, 11C, 11Y, and 11BK, only the BK photosensitive member 11BK on the most downstream side is always in contact with the transfer belt, and the remaining photosensitive drums 11M, 11C and 11Y can contact and separate from the transfer belt.

Hereinafter, image formation of the laser printer according to the present embodiment will be described.
A multicolor image forming mode for forming a color image on the transfer paper will be described. The four photosensitive drums 11M, 11C, 11Y, and 11BK are in contact with the transfer belt 60, respectively. The electrostatic adsorption roller 61 applies a charge having the same polarity as the toner to the transfer paper 100, and the transfer paper 100 is adsorbed to the transfer belt 60. As a result, as described above, transfer failure of the toner image due to charge-up of the transfer material can be eliminated.

  The transfer paper 100 is conveyed while adsorbed to the transfer belt 60, and magenta, cyan, and yellow color toner images formed on the upstream color drums 11M, 11C, and 11Y are sequentially superimposed and transferred. The black toner image formed on the BK drum 11BK is superimposed and transferred. The toner image transferred and superimposed on the transfer paper 100 is fixed by the fixing unit 7 to form a permanent full-color image.

  In the single color image forming mode in which, for example, a black single color image is formed on the transfer paper 100, the color drums 11Y, 11C, and 11M are separated from the transfer belt 60 in FIG. Only the BK drum 11BK is brought into contact with the transfer belt 60. The transfer paper 100 is conveyed to the transfer nip of the BK drum 11BK, and after the black toner image is transferred, the transfer paper 100 is fixed by the fixing unit 7 to form a black monochrome image.

  EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to these.

[Example 1]
(Machine conditions)
Gap between development sleeve and photosensitive drum (Gp) 0.5mm
Gap between development sleeve and doctor blade (Gd) 0.75mm
Development sleeve diameter φ18mm
Photoconductor linear speed 125mm / sec
Ratio of linear velocity of developing roller to linear velocity of photoreceptor 1.5
Toner concentration detection sensor Magnetic permeability sensor (Toner condition)
Polyol resin Weight average particle size 6-7μm
External additive 1.85wt%
(Carrier conditions)
Acrylic resin solution (solid content 50% by weight) 56.0 parts Guanamine solution (solid content 77% by weight) 15.6 parts Alumina particles [0.3 μm, specific resistance 10 ¹⁴ (Ω · cm)] 160.0 parts Toluene 900 Part 900 parts of butyl cellosolve was dispersed with a homomixer for 10 minutes to prepare a coating film forming solution, which was coated on a carrier core material surface with a Spira coater (Okada Seiko Co., Ltd.) to a film thickness of 0.15 μm and dried. . The obtained carrier was baked by standing in an electric furnace at 150 ° C. for 1 hour. After cooling, the ferrite powder bulk was crushed using a sieve having an opening of 100 μm to obtain a carrier. The measurement of the binder resin film thickness was performed by observing the cross section of the carrier with a transmission electron microscope so that the coating film covering the carrier surface could be observed. As the core material for the carrier, a carrier having a size of at least 20 μm (average particle diameter) is used in order to prevent carrier adhesion (scattering) to the electrostatic latent image carrier, and carrier streaks are generated. From the standpoint of preventing image quality deterioration such as prevention, a film having a thickness of 100 μm at most is used. Specific materials that are known as two-component carriers for electrophotography, such as ferrite, magnetite, iron, nickel, etc., may be appropriately selected according to the use and purpose of use of the carrier.
The carrier thus obtained was set in a commercially available digital full-color copier (Ricoh's ipsioColor 8000), and a black solid white color (a document with no image as the most extreme stress of a low image area) was run 900 sheets Evaluation was performed. The evaluation results are shown in Table 1. 3 and 4 show the results of measuring changes in the output (Vt) of the permeability sensor during running and changes in the bulk specific gravity of the developer.

[Example 2]
The mechanical conditions and toner conditions are the same as in Example 1, but the carrier conditions are different.
(Carrier conditions)
Silicone resin solution [solid content 15% by weight]
(SR 2411: manufactured by Toray Dow Corning) 227 parts γ- (2-aminoethyl) aminopropyltrimethoxysilane 6 parts Alumina particles [0.3 μm, specific resistance 10 ¹⁴ (Ω · cm)] 160 parts Toluene 900 parts Butyl cellosolve 900 The part was dispersed with a homomixer for 10 minutes, a coating film forming solution was prepared, applied to the surface of the carrier core material with a Spira coater (Okada Seiko Co., Ltd.) so as to have a film thickness of 0.15 μm, and dried. The obtained carrier was baked in an electric furnace at 300 ° C. for 2 hours. After cooling, the ferrite powder bulk was crushed using a sieve having an opening of 100 μm to obtain a carrier. Using the carrier thus obtained, running evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

Example 3
The mechanical conditions and toner conditions are the same as in Example 1, but the carrier conditions are different.
(Carrier conditions)
Acrylic resin solution (solid content 50% by weight) 56.0 parts Guanamine solution (solid content 77% by weight) 15.6 parts Silica particles [0.2 μm, specific resistance 10 ¹³ (Ω · cm)] 160.0 parts Toluene 900 900 parts of butyl cellosolve was dispersed with a homomixer for 10 minutes to prepare a coating film forming solution, which was applied to the surface of the carrier core material by a Spira coater (Okada Seiko Co., Ltd.) so as to have a film thickness of 0.10 μm and dried. . The obtained carrier was baked by standing in an electric furnace at 150 ° C. for 1 hour. After cooling, the ferrite powder bulk was crushed using a sieve having an opening of 100 μm to obtain a carrier. Using the carrier thus obtained, running evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

Example 4
The mechanical conditions and toner conditions are the same as in Example 1, but the carrier conditions are different.
(Carrier conditions)
Acrylic resin solution (solid content 50% by weight) 30.0 parts Guanamin solution (solid content 77% by weight) 8.3 parts Silica particles [0.2 μm, specific resistance 10 ¹³ (Ω · cm)] 160.0 parts Toluene 900 Part 900 parts of butyl cellosolve was dispersed with a homomixer for 10 minutes to prepare a coating film forming solution, which was applied to the surface of the core material of the carrier with a Spira coater (Okada Seiko Co., Ltd.) so as to have a film thickness of 0.08 μm and dried. . The obtained carrier was baked by standing in an electric furnace at 150 ° C. for 1 hour. After cooling, the ferrite powder bulk was crushed using a sieve having an opening of 100 μm to obtain a carrier. Using the carrier thus obtained, running evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

Example 5
The mechanical conditions and toner conditions are the same as in Example 1, but the carrier conditions are different.
(Carrier conditions)
Acrylic resin solution (solid content 50% by weight) 30.0 parts Guanamin solution (solid content 77% by weight) 8.3 parts Silica particles [0.2 μm, specific resistance 10 ¹³ (Ω · cm)] 160.0 parts Toluene 900 Part 900 parts of butyl cellosolve was dispersed with a homomixer for 10 minutes to prepare a coating film forming solution, which was applied to the surface of the core material of the carrier with a Spira coater (Okada Seiko Co., Ltd.) so as to have a film thickness of 0.03 μm and dried. . The obtained carrier was baked by standing in an electric furnace at 150 ° C. for 1 hour. After cooling, the ferrite powder bulk was crushed using a sieve having an opening of 100 μm to obtain a carrier. Using the carrier thus obtained, running evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

[Comparative Example 1]
The mechanical conditions and toner conditions are the same as in Example 1, but the carrier conditions are different.
(Carrier conditions)
Acrylic resin solution (solid content 50% by weight) 56.0 parts Guanamin solution (solid content 77% by weight) 15.6 parts Toluene 900 parts Butyl cellosolve 900 parts are dispersed with a homomixer for 10 minutes to prepare a coating film forming solution. Then, it was applied to the surface of the carrier core material with a Spira coater (Okada Seiko Co., Ltd.) so as to have a film thickness of 0.15 μm and dried. The obtained carrier was baked by standing in an electric furnace at 150 ° C. for 1 hour. After cooling, the ferrite powder bulk was crushed using a sieve having an opening of 100 μm to obtain a carrier. Using the carrier thus obtained, running evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1. 3 and 4 show the results of measuring changes in the output (Vt) of the permeability sensor during running and changes in the bulk specific gravity of the developer.

[Comparative Example 2]
The mechanical conditions and toner conditions are the same as in Example 1, but the carrier conditions are different.
(Carrier conditions)
Acrylic resin solution (solid content 50% by weight) 56.0 parts Guanamine solution (solid content 77% by weight) 15.6 parts Titanium oxide particles [0.02 μm, specific resistance 10 ⁷ (Ω · cm)] 26.7 parts Toluene 900 parts Butyl cellosolve 900 parts are dispersed with a homomixer for 10 minutes to prepare a coating film forming solution, which is coated on a carrier core material surface by a Spira coater (Okada Seiko Co., Ltd.) to a film thickness of 0.15 μm and dried. did. The obtained carrier was baked by standing in an electric furnace at 150 ° C. for 1 hour. After cooling, the ferrite powder bulk was crushed using a sieve having an opening of 100 μm to obtain a carrier. Using the carrier thus obtained, running evaluation was performed in the same manner as in Example 1, and the results are shown in Table 1.

3 and 4, Example 1 containing alumina particles, the specific resistance of the alumina particles being 10 ¹⁴ (Ω · cm), D / h being 2.0, and the particle content being 80 wt% is shown in FIG. Good results were obtained with little change in the bulk specific gravity of the agent and almost no change in the output of the magnetic permeability sensor. Although not shown in FIGS. 3 and 4, alumina particles or silica particles are contained, the specific resistance of these particles is 10 ¹² (Ω · cm) or more, 1 <D / h <10, particle content rate From Table 1 above, Examples 2 to 5 having a content of 50 to 95 wt% showed good results with small changes in the bulk specific gravity of the developer as in Example 1.
On the other hand, from FIG. 3 and FIG. 4, in the modified example 1 containing no particles, the change in the bulk specific gravity of the developer was larger than that in the example 1, and the output fluctuation of the magnetic permeability sensor was also large, and good results were not obtained. Although not shown in FIGS. 3 and 4, the particles are titanium oxide, the specific resistance of the particles is 10 ¹² (Ω · cm) or more, 1 <D / h <10, and the particle content is 50 to 50%. From Comparative Example 2, which does not satisfy the requirement of 95 wt%, from Table 1 above, similar to Comparative Example 1, the bulk specific gravity variation of the developer was large, and good results were not obtained.

  As described above, in the image forming apparatus according to the present embodiment, the change in the bulk specific gravity of the developer caused by a cause other than the toner concentration can be suppressed, so that stable toner concentration control can be performed.

In this embodiment, a magnetic permeability sensor, which is a kind of bulk density sensor, is used as the toner density sensor. However, since fluctuations in bulk specific gravity have also been solved, the bulk density sensor other than the magnetic permeability sensor can be used stably. The toner density can be controlled.
In this embodiment, an example in which the image forming apparatus is applied to a color laser printer has been described. However, the present invention can be applied not only to a color image forming apparatus but also to a monochrome image forming apparatus.

As described above, in the developing unit as the developing device, the bulk density sensor is a magnetic permeability sensor. Therefore, when the carrier is used in combination with a developing device that controls the toner density based on the detected value of the magnetic permeability sensor, even if the developer is used in a state where a high stress is applied, it cannot be obtained by the conventional technology. Stable toner density control has become possible.
In the developing unit as the developing device, the specific resistance of the particles is 10 ¹² (Ω · cm) or more. Therefore, even if the particles are exposed to the surface while having contact with the core material, charge leakage can be suppressed, so that stable chargeability can be obtained, especially when the developer is stored for a long period of time, and the decrease in the charge amount is suppressed. The improvement effect is remarkable. On the other hand, when the specific resistance of the particles is less than 10 ¹² (Ω · cm), charge leakage cannot be suppressed, so that stable chargeability cannot be obtained. Also, as mentioned in the above prior art, it is a technique similar to the present invention, which is different from the one in which conductive particles larger than the coating resin film thickness are contained in the coating film (Japanese Patent Laid-Open No. 9-160304). As an example, the resistance of particles to be included in the coating film can be mentioned. In this technique, in order not to increase the resistance of the carrier, the particles are used as a conductive path, and the resistance value is preferably 10 ¹⁰ or less. However, in the present invention, as described above, the particles are not used as a conductive path. That is, in the present invention, the particles are not used as a resistance adjusting material as in the prior art, but are used as a protective material for the coating film resin and a surface shape adjusting material. In addition to the particles listed here, any particles having a specific resistance of 10 ¹² (Ω · cm) or more can be used.
Moreover, the effect is remarkable because a particle | grain is an alumina and the content rate is the range of 50-95 wt% of a coating film composition component, Preferably it is 70-90 wt%. Furthermore, the effect is remarkable when the particles are silica and the content thereof is in the range of 50 to 95 wt% of the coating film composition component, preferably 70 to 90 wt%. A mixture of alumina and silica may also be used. When the content of the particles is less than 50 wt%, since the proportion of the particles is smaller than the proportion of the binder resin on the surface of the carrier particles, both the carrier charge-up relaxation effect and the spacer effect are small. This is not preferable because sufficient bulk density stability cannot be obtained. On the other hand, if it is more than 95 wt%, the proportion of the binder resin on the surface of the carrier is too much for the particles to occupy, so the proportion of the binder resin that is the charge generation location becomes insufficient, Insufficient charging ability. In addition, since the amount of particles is too large compared to the amount of binder resin, the ability to hold particles by the binder resin becomes insufficient, and the particles are easily detached, which is not preferable because sufficient durability cannot be obtained. Further, although similar to the above-mentioned present invention (Japanese Patent Laid-Open No. 9-160304), the particle content range is different from that of the present invention, and the technique is “0.01 to 50% by weight of the coating resin”. That is, when converted to the content rate calculation method of the present invention, it is “0.01 to 33.33 wt% of the coating film composition component”. In this case, the durability is improved as compared with the conventional case, but as described above. As described above, since the proportion of the binder resin on the surface of the carrier particle is small, the charge up relaxation effect of the carrier and the spacer effect are small, so that sufficient bulk density stability cannot be obtained, which is not preferable. . The coating resin is not specified at all, and any commonly used resin can be used.
Further, the alumina of the present invention is preferably 10 μm or less of alumina particles, and any particles that have not been surface-treated or those that have been surface-treated such as hydrophobizing treatment can be used. As the silica of the present invention, those used for toner and those other than that can be used, and those not subjected to surface treatment and those subjected to surface treatment such as hydrophobic treatment can be used. Carbon black or an acidic catalyst can be used alone or in combination as a charge and resistance control agent. Any carbon black that is commonly used for carriers or toners can be used. As the acidic catalyst, one having a catalytic action can be used. For example, it has a reactive group such as a fully alkylated type, a methylol group type, an imino group type, and a methylol / imino group type, but is not limited thereto.

1 is a schematic configuration diagram of a laser printer according to an embodiment. FIG. 2 is an enlarged view showing a schematic configuration of magenta image forming means in the printer according to the present embodiment. The graph which shows the output (Vt) fluctuation | variation of a magnetic permeability sensor when performing running evaluation using the carrier obtained in Example 1 and Comparative Example 1, respectively. The graph which shows transition of the bulk specific gravity of a developer when running evaluation is performed using the carrier obtained in Example 1 and Comparative Example 1, respectively.

Explanation of symbols

1M, 1C, 1Y, 1BK Image forming means 5 Registration roller pair 6 Transfer unit (transfer conveyance device)
9 Reversing unit 10M, 10C, 10Y, 10BK Photosensitive unit 11M, 11C, 11Y, 11BK Photosensitive drum 12M Lubricant application and static elimination brush roller 13M Cleaning blade 15M Charging roller 20M Development unit 26M Magnetic permeability sensor 28M Developer 60 Transfer belt 61 Electrostatic attracting roller (Electrode member for attracting transfer material)
100 transfer paper

Claims (6)

A developer comprising at least a toner comprising a binder resin and a pigment, and a carrier having a coat film having at least the binder resin and particles;
Toner concentration detecting means for detecting the toner concentration of the developer;
In a developing device comprising a control means for controlling the toner density based on the detection result of the toner density detection means,
Using a bulk density sensor as the toner concentration detection means,
And the particle diameter (D) of the particles and the film thickness (h) of the binder resin are:
A developing device satisfying a relationship of 1 <[D / h] <10. The developing device according to claim 1.
The developing device, wherein the bulk density sensor is a magnetic permeability sensor. The developing device according to claim 1 or 2,
A developing device characterized in that the specific resistance of the particles is 10 ¹² (Ω · cm) or more. The developing device according to claim 1, 2 or 3,
A developing device, wherein the particles are at least one of alumina and silica. The developing device according to claim 1, 2, 3 or 4,
A developing apparatus, wherein the content of the particles is 50 wt% or more and 95 wt% or less of the coating film composition component. An image carrier;
Latent image forming means for forming a latent image on the image carrier;
In an image forming apparatus having a developing unit that develops a latent image formed on the image carrier using a two-component developer containing toner and a carrier,
An image forming apparatus using the developing device according to claim 1, 2, 3, 4 or 5 as the developing means.

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