JP2006308732A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem; when images having a high printing ratio are continuously printed in a small developing unit using a small amount of a developer including a toner by an emulsion polymerization-agglomeration method or a toner having a charge control agent content of ≤1 wt.%, the toner charge amount is reduced and toner flying-off and fogging occur. <P>SOLUTION: In a developing device, a relationship of 2≤h/d≤3.5 is satisfied, wherein d represents the shortest distance DSD (mm) between a photoreceptor and a sleeve, and h represents the average spike height (mm) of a magnetic brush on the developer bearing member in a state where the electrostatic latent image holding member is not faced to the developer bearing member in a development position. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a developing device using a two-component developer composed of toner and a carrier used in an image forming apparatus such as a copying machine, a printer, and a facsimile machine.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus that exposes a uniformly charged photoreceptor, which is an electrostatic latent image holding member, forms an electrostatic latent image, and visualizes it with toner, which is colored particles, has a high speed. Since image formation is possible, it is widely used in digital printers and copiers.

  In recent years, there has been a particularly increasing demand for colorization, and even in an electrophotographic image forming apparatus, a full-color image forming apparatus composed of toner images of four colors of cyan, magenta, yellow and black has been realized. In such an electrophotographic image forming apparatus, in recent years, there is an increasing demand for downsizing of the apparatus main body in order to achieve space saving in addition to high speed and high image quality.

On the other hand, as a developer used for developing an electrostatic latent image, a two-component developer composed of a magnetic carrier and a toner capable of realizing high image quality and low running cost is widely used. A developing device comprising a developer carrying member having a sleeve slides the developer onto the surface of the photosensitive drum in the form of a magnetic brush to develop the electrostatic latent image formed on the drum surface. ing.
In order to realize downsizing of the apparatus, there is a growing demand for downsizing of the developing device. With this miniaturization, it is necessary to reduce the amount of developer in the developing device. M / L is 9 g / cm or less when the amount of developer is M (g) and the axial length carrying the developer on the developer carrier is L (cm). For example, in a developing device having a printing width of A4 vertical feed, it is desired to realize a small amount of developer with a developed image amount of 200 g or less.

  In addition, in the toner, wax, which is a release component, is encapsulated in the toner, and the surface of the toner is smoothed by coating with a resin having a high releasability on the surface, and transfer performance from the electrostatic latent image holding member to the transfer member In recent years, toners using an emulsion polymerization aggregation method have been frequently used because it is easy to ensure cleaning performance with a blade or the like by controlling the shape.

  Further, in order to ensure the surface releasability, it is of course important to reduce the presence of the release agent component on the surface, but it is also important to reduce the amount of charge control agent that has been used conventionally. is there.

  Further, for the purpose of cost reduction, a toner in which the amount of the charge control agent having a high cost is reduced to 1 wt% or less is desired.

  However, conventionally, when the amount of the developer is reduced as described above, a large amount of toner is consumed particularly when an image with a high printing rate is continuously printed, and the toner density, which is the ratio of the toner to the carrier, rapidly decreases. Therefore, it is necessary to replenish toner rapidly.

  At this time, if the toner by the above-described emulsion polymerization aggregation method or the toner having a charge control agent of 1 wt% or less is used, the charging ability of the toner itself is low. As a result, fogging of toner adhesion, rotation of the developer carrying member, scattering of toner floating in the air, and an increase in image density occur. In addition, there is a problem that the toner consumption amount increases other than the image area, and a problem that the frequency of replacement of the waste toner collecting portion which is an unnecessary toner increases.

  On the other hand, in order to prevent rapid replenishment of toner, it is conceivable to use a toner with a high ratio of toner to carrier. However, it does not solve the problem of fogging, toner scattering, and density increase as described above.

  Among them, in a small developing device with a small amount of developer, various toners are used to prevent fogging, toner scattering and density increase while ensuring the toner charge amount after toner replenishment when continuously printing images with a high printing rate. Many methods have been studied.

  In the developer and the developing device of (Patent Document 1), a developer is proposed in which the toner coverage on the carrier surface calculated by the average particle diameter of the toner and carrier is 30 to 65%, and conductive silica is externally added. Has been. According to this developing device, the charge transfer speed between the carrier and the toner can be increased by the effect of the conductive silica, and the fog and toner scattering can be prevented while ensuring the image density by preventing the generation of weakly charged toner. Can be prevented.

  In the developing device of (Patent Document 2), a developing device in which a paddle using a specific configuration other than a screw is arranged as a device for mixing and stirring a developer has been proposed. It is described that the mixing and stirring property of the developer is improved by the function of the paddle.

  In the developing device of (Patent Document 3), a developing device in which a needle-shaped stirring member is provided on a screw has been proposed. The mixing stirring of the developer is promoted by the needle-shaped stirring member.

  In the developing device of (Patent Document 4), a screen member on a mesh is attached to a screw, and the developer is agitated and appropriately charged by friction between the toner and the carrier.

In the developing device of (Patent Document 5), the developer is agitated by providing a specific projecting member on the screw, and appropriate charging is performed by friction between the toner and the carrier.
Japanese Patent Laid-Open No. 11-194525 JP 2000-19845 A JP 2004-333658 A JP-A-10-63081 JP 2000-19823 A

  However, in the above-mentioned prior art (Patent Document 1), when the conductive agent silica is added to make full use of the developer having a high toner concentration, it is possible to reduce obvious uncharged toner and low-charged toner. Thus, the movement of the charge between the toner and the carrier is accelerated, a high charge amount cannot be obtained, and when the toner is moved from the electrostatic latent image holding member to the transfer member, the toner is likely to scatter and is a minute dot. There arises a problem that the reproducibility of isolated dots is deteriorated. Further, when the toner concentration is high, the replenished toner has a small contact probability with the carrier, and there is a limit to the promotion of charge transfer due to the effect of the conductive agent. Therefore, when toner is replenished rapidly, problems such as toner scattering and fogging occur.

  Further, when the paddle is arranged in (Patent Document 2), there is a problem that the size of the developing device increases due to an increase in the number of components. In addition, in the portion immediately after the developer rapidly replenished with toner moves from the screw on the toner replenishment side to the screw on the developer carrier side, the developer is not sufficiently agitated and the toner is charged. The amount decreases, causing fogging, toner scattering, and an increase in image density.

  Furthermore, in (Patent Document 3), (Patent Document 4), and (Patent Document 5), a technique for enhancing the mixing and stirring properties of a carrier and a toner is used. Is increased, the force to push the developer in the screw rotation direction is increased, the developer is weakened in the conveying force, and the circulation speed is decreased. In this case, when continuous solid printing is performed, the probability of contributing to the development of the developer in the vicinity of the developer carrying member increases, causing a problem that the toner density decreases rapidly and the image density decreases. A method of improving the stirring performance of only the screw on the toner supply side is also conceivable, but in this case, a large amount of developer stays in the screw portion on the toner supply side, and as a result, the developer on the developer carrier side decreases, and a solid image Etc., the toner density rapidly decreases, and the same problem as described above that the image density decreases occurs.

  The present invention solves the above technical problem, and in a small developing device containing 1 wt% or less of toner and charge control agent in the emulsion polymerization aggregation method, fogging to a non-image portion is performed even when toner is rapidly replenished. The present invention provides a two-component developing device with high image quality that has good dot reproducibility without causing toner scattering and image density increase.

    In order to solve this problem, the invention according to claim 1 is a toner prepared by an emulsion polymerization aggregation method, or a toner having a charge control agent content of 1 wt% or less, a developer comprising a carrier, An electrostatic latent image holder that forms and rotates an electrostatic latent image, and a plurality of magnetic field generating means, and holds a magnetic brush formed of the developer for visualizing the electrostatic latent image. A developer carrying member that contacts the electrostatic latent image holding member, wherein the total weight of the developer in the apparatus is M (g), and the developer on the developer carrying member is carried. M / L is 3 g / cm or more and 9 g / cm or less when the length in the axial direction is L (cm), and the electrostatic latent image holding member and the developer carrier The current distance DSD is d (mm) and the electrostatic latent image holder is not opposed to the developing position. Provided is a developing device characterized by satisfying a relationship of 2 ≦ h / d ≦ 3.5, where h (mm) is an average spike height of the magnetic brush on the agent carrier. .

  By providing a specific relationship between the average brush height of the magnetic brush and the closest distance between the electrostatic latent image holding member and the sleeve, a developer pool is generated in the upstream portion of the development nip.

  At this portion, the developer is disturbed and the charging of the toner is sufficiently promoted. As a result, even when the toner is replenished rapidly in order to secure the toner concentration, it is possible to prevent the occurrence of toner scattering, fogging and an increase in image density.

  On the other hand, if h / d is less than 2, a developer pool is not formed on the upstream side of the development nip, the effect of disturbing the developer is reduced, and the effect of improving the toner charge amount is reduced. On the other hand, if h / d exceeds 3.5, a large stress is applied to the developer in the developer pool portion, causing a problem that the developer deteriorates.

  According to the second aspect of the present invention, the developer carrying member is positioned above the electrostatic latent image holding member, and the angle formed between the line connecting the center of the electrostatic latent image holding member and the developer carrying member and the horizontal line is The present invention provides a developing device characterized by being 30 degrees or more and 150 degrees or less.

  The developer carrying member is positioned above 30 ° to 150 ° from the horizontal direction above the electrostatic latent image holding member, so that the developer gets on the electrostatic latent image holding member by gravity, and is thus developed. The developer pool formed upstream of the nip portion is further disturbed, and toner charging is promoted. As a result, even when the toner is replenished rapidly, it is possible to prevent the occurrence of toner scattering, fogging and an increase in image density.

  At this time, when the angle is less than 30 degrees or exceeds 150 degrees, the developer does not lean against the electrostatic latent image holding body due to gravity, and the disturbance effect from the electrostatic latent image holding body is small, and the toner charge amount improving effect is improved. Less.

  According to a third aspect of the present invention, there is provided the developing device characterized in that the developer carrying member has a peripheral speed ratio of 1.3 times or more and 3.0 times or less with respect to the electrostatic latent image holding member. It is to provide.

  In addition, since a speed difference of 1.3 to 3.0 times can be generated between the electrostatic latent image holding member and the developer carrier, the developer pool formed upstream of the developing nip is further disturbed. Charging is promoted. As a result, even when the toner is replenished rapidly, it is possible to prevent the occurrence of toner scattering, fogging and an increase in image density.

  At this time, if the peripheral speed ratio is lower than 1.3 times, it is difficult to obtain the disturbance effect due to the speed difference. Further, when the peripheral speed ratio exceeds three times, a large stress is applied to the developer in the developer accumulation portion, causing a problem that the developer deteriorates.

  According to a fourth aspect of the present invention, the main pole peak position of the developer carrier is not less than 1 degree and not more than 10 degrees upstream from the position facing the electrostatic latent image holding body. A developing device is provided.

  In the developing device of the present invention, the developer reservoir can be easily formed upstream of the developing nip portion by positioning the peak position of the main pole in the upstream direction. Since the developer accumulation amount increases, the developer disturbance time increases, and the charging of the toner can be promoted.

  On the other hand, when the angle exceeds 10 degrees, the long portion of the magnetic brush is positioned upstream of the rotation, and the developer pool becomes small. As a result, the toner charge promoting effect is reduced.

  According to a fifth aspect of the present invention, there is provided a developing device comprising magnetic field generating means for attracting the developer of the magnetic brush at least in the vicinity of the developer carrying member inside the electrostatic latent image holding member. is there.

  In the developing device of the present invention, since the developer is attracted to the electrostatic latent image holding member side and the amount of developer accumulation increases, the disturbance time of the developer is further increased, and toner charging can be promoted.

  According to a sixth aspect of the present invention, there is provided a developing device having at least a fluorine-modified silicone resin or a fluorine-modified acrylic resin on the surface of a resin carrier.

  By using a resin modified with fluorine on the surface of the carrier, the flowability of the developer can be increased. As a result, the developer in the developer pool is easily moved, and charging of the toner is promoted.

Further, the invention according to claim 7 is at least an electrostatic latent image holding member capable of rotating by forming an electrostatic latent image on the surface;
In order to visualize the electrostatic latent image, when the powder projection area is A, the absolute maximum length of the powder is M, and the shape factor (SF-1) of the powder is expressed by (Expression 1), The present invention provides a developing device using toner having a shape factor (SF-1) of 100 or more and 150 or less.

  In the developing device of the present invention, the spherical toner exhibits a roller function in the developer reservoir, and the developer is further disturbed to promote toner charging. When the shape factor (SF-1) value exceeds 150, it becomes difficult for the toner to function as a roller.

As described above, when the developer amount is M (g) and the axial length carrying the developer on the developer carrier is L (cm), the M / L is 3 g. In a developing device using a small two-component developing device having a density of / cm or more and 9 g / cm or less and an emulsion polymerization aggregation toner or a toner having a charge control agent of 1 wt% or less,
By providing an average height of the magnetic brush and a specific distance between the electrostatic latent image holder and the developer carrier, a developer pool is formed at the upstream position of the developing unit, and the developer is disturbed. Provides a high-quality small two-component developing device that promotes toner charging, promotes toner charging even when a solid image is printed and toner is rapidly replenished, and prevents fogging, toner scattering, and increase in image density To do.

  Hereinafter, a developing device according to the present invention will be described based on preferred embodiments with reference to the accompanying drawings.

(Embodiment 1)
As shown in FIG. 1, the image forming apparatus according to the first embodiment of the present invention is held between the photosensitive drums 1Y and 1M by the support 2Y and comes into contact with the peripheral surface of the upstream photosensitive drum 1Y. A cleaning blade 3Y for removing the toner remaining on the surface of the body drum 1Y is disposed, and the developing roller 4M for adhering the toner to the peripheral surface of the adjacent photosensitive drum 1M has an axial center above the support 2Y. Further, they are arranged so as to be positioned on a line segment inclined toward the support 2Y side from the axis of the adjacent upstream photosensitive drum 1Y, and the members of other colors are also arranged in the same manner. With this arrangement, the pitch between the photosensitive drums 1Y, 1M, 1C, and 1K is shortened, and the apparatus is downsized.

Hereinafter, the configuration thereof will be described using the magenta developing device 8M, but the same applies to the developing devices 8Y, 8C, and 8K of other colors, and the description thereof will be omitted. The photoconductive drum 1M is a laminated organic photoconductor having an outer diameter of 24 mm, and rotates at a peripheral speed of 100 mm / s. The photosensitive drum 1M has a charging roller 5M for charging the photosensitive drum 1M while being driven to rotate by the photosensitive drum 1M, and a toner image formed on the photosensitive drum 1M for transferring to the intermediate transfer belt 11. A first transfer roller 6M is disposed. The charging roller 5M uses an outer diameter of 10 mm and a metal shaft formed with epichlorohydrin rubber, and the first transfer roller 6M uses an outer diameter of 12 mm and a metal shaft formed with a conductive urethane sponge. The intermediate transfer belt 11 was a polycarbonate sheet having an electric resistance of 1 × 10 ⁹ Ω · cm.

  An electrostatic latent image is formed by irradiating the surface of the photosensitive drum 1M uniformly charged by the charging roller 5M with a laser beam (not shown) according to image information, and then the developing area ( The developer magnetic brush conveyed between the developing roller 4M and the photosensitive drum 1M is rubbed against the electrostatic latent image, and only the toner moves to the surface of the photosensitive drum 1M to form a toner image. The laser power was 280 μW, a DC voltage of 1.2 kV was applied to the charging roller 5M, and the charged potential V0 and the post-exposure potential VL of the photosensitive drum 1M were measured to be −650V and −100V, respectively. . A bias voltage in which a rectangular wave AC voltage having a frequency of 3 kHz and a peak-to-peak voltage of 1.5 kV is superimposed on a DC voltage of −500 V is applied to the developing roller 4M.

  The toner image formed on the photosensitive drum 1M is transferred to the surface of the intermediate transfer belt 11 by the first transfer roller 6M to which a voltage of +600 V is applied. The above operation is performed for the image forming unit including the developing devices 8Y, 8M, 8C, and 8K for yellow, magenta, cyan, and black and the photosensitive drums 1Y, 1M, 1C, and 1K, and the four colors are combined on the intermediate transfer belt 11. A toner image is formed. Thereafter, the composite toner image is collectively transferred by the second transfer roller 7 onto the recording paper 10 conveyed from the recording paper tray 9, and heat, pressure, etc. are provided by the fixing device 12 provided on the discharge path of the recording paper 10. Is fixed on the surface of the recording paper 10 by the known means. On the other hand, the toner remaining on the surface of the photoconductive drum 1M is removed from the surface of each photoconductive drum 1M after the transfer of the toner image is completed by a cleaning blade 3M in which urethane rubber is formed into a sheet shape. One cycle of formation is complete.

  Hereinafter, the developing device according to Embodiment 1 of the present invention will be described in more detail using the developing device 8M with reference to FIG. The same applies to the developing devices 8Y, 8C, and 8K for other colors.

  The magenta toner used in the study was prepared by an emulsion polymerization aggregation method using 85 wt% of styrene butyl acrylate resin, 10 wt% of olefin wax, and 5 wt% of quinacridone pigment, and the volume average particle size was 5.5 μm. Non-magnetic toner base particles were obtained. The toner base particles 98.5% by weight were externally added (mixed) with 1.0% by weight of hydrophobic silica and 0.5% by weight of hydrophobic titania as external additives. The shape factor SF value of the toner calculated in the above (Equation 1) was 160.

As a carrier, a dimethyl silicone resin was coated on the surface of a Mn ferrite having a volume average particle diameter of 35 μm as a core material. The volume resistance value was 2 × 10 ¹⁰ Ω · cm, the specific gravity was 5.0 g / cm ³ , and the magnetization was 61.9 Am ² / kg.

  The carrier and the toner were mixed to prepare 88 g of developer. The developer was 81 g of carrier and 7 g of toner, the toner concentration was 8%, and a 100 cc container was prepared and mixed for 10 minutes in a ball mill.

  As shown in FIG. 2, the developing device according to the first embodiment is divided into two developer transport paths by a partition wall 13M, and is located above the partition wall 13M on the far side from the developing roller 4M. A first developer transport path 14M is provided, and a second developer transport path 15M is provided on the lower side of the partition wall 13M and closer to the developing roller 4M. An outward projecting portion 16M is formed in the second developer conveying path 15M, and a developing roller 4M projects from the projecting portion 16M. Here, the developing roller 4M is composed of seven magnets fixedly arranged in a rotatable aluminum developing sleeve 26M having a surface roughness Rz of 5 μm. These seven magnets are arranged so that a magnetic force peak is formed in the developing region where the developing roller 4M and the photosensitive drum 1M are close to each other, and a magnetic force valley is formed around the panning shaft 25M. In the present embodiment, the N pole is arranged in the development region, the main pole magnetic force is 90 mT, and the panning shaft 25M is sandwiched between the S pole and the N pole. Further, an area where the magnetic force is almost zero is provided in the area where the second developer conveyance path 15M is close so that the south poles are adjacent to each other so that the developer after the development can be effectively peeled off. In order to make the magnetic force in this region as close to zero as possible, it is important to make the distance between magnets of the same polarity as large as possible. The magnetic force in this peeling region was measured, and it was confirmed that the magnetic force was 5 mT or less.

  In addition, the center of the development main electrode is positioned at the closest part of the photoreceptor. When the central part of the developing main pole is located closest to the photoreceptor, the main pole magnetic pole angle is 0 degree, and the angle when the developing main pole is located in the downstream direction of the sleeve is expressed by +, and the case of the upstream side of the rotation is expressed. - In this developing apparatus, the main pole magnetic pole angle was set to 0 degree.

  The outer diameter of the developing roller 4M is 14 mm, the axial length of the portion carrying the developer is 220 mm, and the developing sleeve 26M has a width of 120 mm / s with respect to the rotation direction of the photosensitive drum 1M. The circumferential speed ratio is 1.2 with respect to the photosensitive drum 1M. The developing roller 4M and the photosensitive drum 1M are arranged so as to face each other, and the gap between the developing roller 4M and the photosensitive drum 1M can be adjusted by changing the diameters of the rollers 18M provided on both sides of the developing roller 4M. In the first embodiment of the present invention, the gap between the developing roller 4M and the photosensitive drum 1M in the developing region is adjusted to 0.4 mm. M / L was 4 g / cm, where M (g) was the developer amount, and L (cm) was the axial length carrying the developer on the developer carrier.

  Further, the angle θ created by the line connecting the center of the photosensitive drum 1M and the center of the developing roller 4M and the horizontal line is 20 degrees.

  In addition, a second conveying screw 17M extending along the axial direction is provided in the second developer conveying path 15M located below the developing device 8M.

  Furthermore, a first conveying screw 19M that extends along the axial direction of the developing roller 4M is provided in the first developer conveying path 14M of the developing device 8M.

  As shown in FIG. 4, the second conveying screw 17M in the second developer conveying path 15M and the first conveying screw 19M in the first developer conveying path 14M are along the axial direction of the developing roller 4M. The blades or the rotation direction is set so as to convey the developer in opposite directions. For example, the first conveying screw 19M performs the agitating and conveying of the developer in the direction of the arrow X in FIG. The two conveying screws 17M are set so as to convey the developer in the direction of arrow Y in FIG.

  Furthermore, communication ports 20M and 21M that connect the first developer transport path 14M and the second developer transport path 15M are formed at both ends in the longitudinal direction of the developing device 8M. In the communication port 20M located at the tip of the developer conveying direction (X direction) of the first conveying screw 19M, an opening of an appropriate size is formed in the partition wall 13M, and the first The developer that has been stirred and conveyed by the conveying screw 19M falls from the first developer conveying path 14M into the second developer conveying path 15M due to gravity. In the embodiment of the present invention, the outer diameter, the shaft diameter, the screw pitch, and the number of rotations of the first conveying screw 19M and the second conveying screw 17M are set so that the toner is circulated satisfactorily by the two sets of conveying screws. , 12 mm, 5 mm, 25 mm, and 150 rpm, respectively.

  On the other hand, a magnet roller 22M is installed above the communication port 21M located at the tip of the second conveying screw 17M in the developer conveying direction (Y direction) so as to be connected to the end of the first conveying screw 19M. Yes. The magnet roller 22M is coupled so that its axis is coaxial with the rotation axis of the first conveying screw 19M, and its outer diameter is substantially matched with the outer diameter of the first conveying screw 19M. Then, as shown in FIG. 4, the magnet roller 22M is rotated in the same direction as the first conveying screw 19M, and the developer in the second developer conveying path 15M is conveyed in the form of a magnetic brush to the first developer. It is pumping up in the road 14M. The magnet roller 22M in the present embodiment is a rubber in which ferrite or magnetic powder-containing plastic is molded into a roller shape, and N poles and S poles are alternately magnetized in two poles (approximately every 90 °). A magnet is used. In addition, a magnetic member (not shown) such as SUS400 is pasted on both end faces to prevent the developer from adhering to both end faces of the magnet roller 22M and the accompanying clogging of the developer. is doing.

  Further, a separation plate (not shown) is formed integrally with the first developer conveyance path 14M in the vicinity of the magnet roller 22M with respect to the rotation direction of the magnet roller 22M. Further, the separation plate is formed so that its separation surface is inclined with respect to the rotation axis direction of the first conveying screw 19M. Thereby, the developer separated from the magnet roller 22M by the separation surface is smoothly moved in the direction of the first conveying screw 19M. With the configuration described above, the developer is circulated between the second developer transport path 15M located on the lower side and the first developer transport path 14M located on the upper side.

  Further, a toner concentration sensor 23M that detects the toner concentration in the developer from the magnetic permeability of the developer is disposed in the first developer conveyance path 14M, and when the toner concentration decreases due to printing, the toner supply port 24M. The toner is replenished so that the toner density is always controlled to 8%.

  The developer in the second developer conveyance path 15M adheres to the surface of the rotating developing sleeve 26M by a magnetic field from the developing roller 4M to form a magnetic brush, and an aluminum shaft having an outer diameter of 5 mm while rolling on the surface of the developing sleeve 26M. It is transported to a place where the ear cutting shaft 25M is installed. The distance between the developing roller and the auxiliary cutting shaft was 0.3 mm. When the magnetic brush passes through the panning shaft 25M, the average heading height h is adjusted to a length of 1.0 mm, and then reaches the developing region, and the electrostatic brush forms an electrostatic latent image formed on the photosensitive drum 1M. Accordingly, the toner moves to the photosensitive drum 1M and development is performed.

  The developer whose toner density is reduced due to toner consumption by development is transported to the separation region where the magnet pair of the S poles is arranged along with the rotation of the developing sleeve 26M, and is released from the magnetic restraining force on the developing sleeve 26M. In addition, after being removed and conveyed by the second conveying screw 17M, the toner density is adjusted again to 8% while circulating in the first developer conveying path 14M and the second developer conveying path 15M.

  In the present invention, the average spike height h (mm) of the developer is obtained by forming a magnetic brush while rotating the developer alone, and using the microscope (keyence) It was measured by the company make: VHX-100). The average distance from the sleeve reference surface to the average tip end was defined as the average tip height h.

  In the present invention, the particle size distribution of the toner was measured using a Coulter counter (manufactured by Coulter Counter).

  In order to measure the magnetization intensity of the carrier of the present invention, a vibrating sample magnetometer (VSM-P7-15 type: Toei Industry Co., Ltd.) was used. The measurement magnetic field was 79.58 kA / m (1 kOe), and the measurement environment was a temperature of 23 ° C. and a humidity of 50%.

  As a carrier resistance measuring device in the present invention, a super insulation resistance meter SM-8210 (manufactured by Toa DKK Co., Ltd.) was used. The distance between the electrodes was set to 0.4 mm, and magnets having a cross-sectional area of 30 mm × 13 mm were attached to the outer portions of the electrodes so as to face each other. The magnetic force inside the electrode was 60 mT as measured with a gauss meter (HGM8900: manufactured by Toyo Magnetic Industry Co., Ltd.). 0.2 g of carrier was put between the electrodes, a voltage of 50 V was applied, and the resistance value after 30 seconds was measured. The volume resistivity was calculated from the electrode area and the distance between the electrodes. The measurement environment was a temperature of 23 ° C. and a humidity of 50%.

  For measuring the particle size distribution of the carrier of the present invention, LA-920 (manufactured by Horiba, Ltd.) using the principle of laser diffraction / scattering was used as a measuring device. The carrier particle size was measured in a dispersion to which the surfactant sodium lauryl sulfate was added.

  The shape factor SF value of the toner of the present invention was calculated by the above (Equation 1) from the projected area (A) and maximum length (ML) of each toner particle by an optical microscope by an image analysis apparatus. Actually, the average value was obtained after measuring 500 pieces.

  In addition, the charge amount on the developer carrying member was evaluated, and the toner charging performance was evaluated. Using a 795 mesh stainless steel metal mesh, only the toner is sucked and the charge amount is measured with an electrometer 6517A (manufactured by KEITHLEY), and the charge amount Q / m (μC / g) is calculated from the charge amount and the weight change amount. Calculated.

  The solid image density was measured with a reflection densitometer RD914 (manufactured by Macbeth) by extracting 10 points from the image.

  Fogging, which is toner adhesion to the non-image area, was evaluated using a photovolt MODEL 577 (manufactured by Photovolta Inc., USA). The difference between the reflectance of the white part after printing and the reflectance of the new paper was determined.

  The position where the fog and the charge amount are measured is a communication port which is a portion immediately after the developer moves from the screw on the toner supply side of the first developer conveyance path 14M to the developer carrier side of the second developer conveyance path 15M. The fog around 20M (the right end of the image in this study) and the amount of charge at the development nip corresponding to that portion were evaluated. The amount of charge was measured by sampling the fog at a portion 20 mm from the right end of the image and the developer at the right end 20 ± 10 mm of the image.

  Further, as an initial adjustment, the DC voltage of the developing bias was adjusted to set the image density to 1.5, and then the photoreceptor surface potential was adjusted to 150 V with respect to the developing DC bias.

  The evaluation of fog, image density, and charge amount was performed before and after continuous printing of 10 solid images. The evaluation data before and after were compared.

After printing 10 sheets of continuous solids, fog is within 2%, ○, within 1% is ◎, over 2% is x, image density is within a range of 1.5 ± 0.15, 1.5 ± 0 The range of .07 was marked with ◎, and the others were marked with ×.
(Embodiment 1)
Using the developing device as described above, the average height of the head of the developer and the distance D between the photosensitive member and the sleeve are fixed to 0.4 mm, the distance condition between the ear cutting member and the developing roller is changed, and the average of the magnetic brush The h / d was changed from 1.3 to 4.0 while changing the head height h (mm). At the time of initial adjustment, the fog was 0.7 to 0.9% under the respective conditions, the image density was 1.5 ± 0.02, and the charge amount was −26.0 ± 1.0 μC / g. In addition, fog, image density, and charge amount after continuous solid printing of 10 solid images in the initial stage, and fog, image density, and charge after continuous printing of 10 sheets after 30,000 printing. The results of the quantity test are shown in (Table 1).

  It can be seen that initially, h / d is 2.0 to 4.0 or more, fog is 2.0% or less, fog is reduced, and charge amount is increased. That is, by forming an overflow in the front portion of the developing nip, the charge amount is increased, and the reduction of fog can be realized. Further, a print test of 30,000 sheets was performed under these conditions, and h / d was in the range of 2.0 to 3.5, so that fog was small and fluctuations in charge amount and image density could be suppressed. On the other hand, when h / d exceeds 3.5, the charge amount decreases, and it can be seen that an increase in fog and an increase in image density occur.

  When h / D exceeds 3.5, the stress on the developer in the developer pool is increased, and the external additive component of the toner adheres to the carrier, and the charging performance is considered to be deteriorated.

  In the present invention, a tandem (one-pass) color image forming apparatus in which four-color image forming units are arranged in parallel has been taken as an example, but a four-pass developing apparatus in which four-color developing devices are arranged on one photoconductor. It may be a color image forming apparatus or a monochrome image forming apparatus.

  Further, in the present invention, two sets of developer conveying screws are arranged vertically, and the developer is circulated in the vertical direction in the developing device. However, the two sets of developer conveying screws are arranged horizontally. The developer may be circulated horizontally.

  Further, in the present invention, an organic laminated type photoconductor having a negatively charged polarity is used, but a structure using a single layer type organic photoconductor or an a-Si material in which the charge transport layer and the charge generation layer are the same layer. It may be a photoconductor or the like, and the charge polarity of the photoconductor itself may be either negative charge or positive charge. The shape may be a belt shape instead of a drum shape.

  In the present invention, the DC voltage is applied to the charging roller made of epichlorohydrin rubber, but a sine wave or rectangular wave AC voltage may be applied. Urethane rubber, silicone rubber, NBR rubber, acrylic rubber, fluorine rubber, or the like can be used as the charging roller, and surface treatment such as surface coating can be performed as necessary. Further, a scorotron method using a wire and a grid that have been conventionally used or a method using a solid charging element may be used.

  As for the bias voltage applied to the developing roller, it is desirable to set the DC voltage to 50 to 650 V while adjusting the image density or the like as necessary. Further, the toner movement is further facilitated by applying a rectangular wave or sine wave AC voltage having a frequency of 1 to 6 kHz and an amplitude of about 0.2 to 3 kV to promote toner movement. By applying the AC voltage, it is possible to secure the necessary image density, prevent toner adhesion to the non-image area, and improve the fine dot reproducibility.

  In the present invention, the number of magnets inside the developing roller is seven, but a plurality of other magnets may be used. The developing sleeve is also made of aluminum and has a surface roughness Rz of 5 μm, but other nonmagnetic materials may be used. The surface roughness Rz is preferably in the range of 3 to 15 μm from the viewpoint of image uniformity and developer transportability.

  Further, in the present invention, a panning shaft made of a nonmagnetic aluminum shaft having an outer diameter of 5 mm is provided. A magnetic layer regulating member may be used. It is also possible to use a layer regulating member made of a nonmagnetic or magnetic metal plate. Furthermore, a layer regulating member in which a magnetic member is attached to a nonmagnetic plate can also be used.

  In the present invention, the outer diameter of the developing roller, the first conveying screw, the second conveying screw, the screw pitch of each conveying screw, and the number of rotations are not limited to the described values.

  In the present invention, a toner density control method using a magnetic permeability sensor is used. However, a pixel count method in which toner consumption is predicted in advance from an image to be printed and toner is supplied may be used. Further, a method using both the toner density control method and the pixel count method can be considered.

  In the present invention, when the developer amount is M (g) and the axial length carrying the developer on the developer carrier is L (cm), the M / L is 4 g. However, when M / L is less than 3 g / cm, there is little developer, and screw feed unevenness appears on the surface of the developer carrier, and screw unevenness appears in the image. On the other hand, if the M / L exceeds 9 g / cm, the developer amount is 200 g or more, and even if solid images are continuously printed, there is little decrease in toner density, and there are few problems of fogging and toner scattering when rapidly replenished. The device becomes larger.

  In the present invention, the styrene butyl acrylate resin is used as the binder resin, but a polyester resin, an epoxy resin, or a combination of these may be used.

  In the present invention, usable pigments include carbon black, iron black, graphite, nigrosine, azo dye metal complex black pigment, C.I. I. Acetoacetic acid arylamide monoazo yellow pigments such as CI Pigment Yellow 1,3,74,97,98; I. Acetoacetic acid arylamide disazo yellow pigments such as C.I. Pigment Yellow 12, 13, 14, and 17; I. Solvent Yellow 19, 77, 79, C.I. I. Disperse Yellow 164, C.I. I. Red pigments such as CI Pigment Red 48, 49: 1, 53: 1, 57, 57: 1, 81, 122, 5; I. Red dyes such as Solvent Red 49, 52, 58, 8; I. One or two or more kinds of blue dyed pigments of phthalocyanine and derivatives thereof such as Pigment Blue 15: 3 are blended. The addition amount is preferably 3 to 15 parts by weight with respect to 100 parts by weight of the binder resin.

  One or more kinds of charge control agents may be added as necessary for the purpose of charging the toner. About 1% by weight or less of material can be added depending on the purpose of negative charging and positive charging.

  Further, fine particles having an average particle diameter of 5 to 200 nm, such as silica, alumina, and titania, are added for the purpose of improving the charging and fluidity of the toner. If necessary, the surface of the fine particles can be hydrophobized.

  The average toner particle size is desirably 3 to 12 μm. When the particle size is large, it is difficult to achieve high resolution. On the other hand, if the particle size is too small, the toner fluidity is poor and a stable layer cannot be formed, resulting in uneven image density.

  In the present invention, a carrier in which a ferrite core is coated with a resin is used. However, a resin carrier in which magnetic powder is dispersed in a thermosetting binder may be used.

  As the thermosetting binder of the resin carrier, urea resin, melamine resin, polyester resin, epoxy resin and the like can be used in addition to the phenol resin. Since the thermosetting resin is superior in durability, impact resistance, and heat resistance as compared with the thermoplastic resin, a resin carrier composed of a magnetic body and a thermosetting resin taking advantage of these advantages is desired.

The magnetic powder used in the present invention includes ferromagnetic iron oxide particles such as magnetite and maghemite, and spinel ferrite particles containing one or more metals other than iron (Mn, Ni, Zn, Mg, Cu, etc.). A powder, a magnetoplumbite type ferrite particle powder such as barium ferrite, or a fine particle powder of iron or iron alloy having an oxide film on its surface can be used. Ferromagnetic iron oxide particles such as magnetite are preferred. The ferromagnetic iron compound particles preferably have a particle size of 0.02 to 5 μm. The shape may be any of granular, spherical and acicular. Furthermore, the addition amount of the magnetic substance in the thermosetting resin is desirably 50 to 90% by weight. If it exceeds 90% by weight, dispersion in the resin becomes difficult and the magnetic substance is detached. On the other hand, if it is less than 50% by weight, the magnetic force of the carrier becomes small, and there is a problem that the carrier tends to adhere to the toner holding member.
(Embodiment 2)
Using the developing device of the first embodiment, the average heading height of the developer and the distance D between the photosensitive member and the sleeve are fixed to 0.3 mm, the distance condition between the cutting member and the developing roller is changed, and the magnetic brush The h / d was changed from 1.5 to 3.9 while changing the average head height h (mm). At the time of initial adjustment, the fog was 0.6 to 0.8% under the respective conditions, the image density was 1.5 ± 0.03, and the charge amount was −25.5 ± 1.0 μC / g. In addition, fog, image density, and charge amount after continuous solid printing of 10 solid images in the initial stage, and fog, image density, and charge after continuous printing of 10 sheets after 30,000 printing. The results of the quantity test are shown in (Table 2).

  Initially, it can be seen that the fog becomes 2.0% or less, the fog is reduced, and the charge amount is increased under the condition that h / d is 2.0 to 3.9 or more. That is, by forming an overflow in the front portion of the developing nip, the charge amount is increased, and the reduction of fog can be realized. Further, a print test of 30,000 sheets was performed under these conditions, and h / d was in the range of 2.0 to 3.5, so that fog was small and fluctuations in charge amount and image density could be suppressed. On the other hand, when h / d exceeds 3.5, the charge amount decreases, and it can be seen that fogging increases and image density increases.

(Embodiment 3)
In the developing device according to the first embodiment, the angle θ between the photosensitive member center position and the sleeve center position is set to 20 degrees, but this angle is changed to -30 degrees to 180 degrees. Initially, the fog was 0.7 to 0.9% under each condition, the image density was 1.5 ± 0.02, and the charge amount was −26.2 ± 0.9 μC / g. Further, fog and image density and charge amount after continuously printing 10 solid images continuously in the initial stage, and fog and image density after continuously printing 10 sheets after printing 30,000 sheets. The results of the charge amount test are shown in Table 3. From 30 degrees to 150 degrees, it was confirmed that particularly good results were obtained with respect to fog and that the charge amount was also high. Furthermore, a printing test of 30,000 sheets was performed under the favorable conditions of 30 ° to 150 °. Even after printing 30,000 sheets, a high charge amount was maintained, fog was small, and image density was stable. Due to the positional relationship between the photosensitive member and the developing roller, charging is promoted particularly when the developing roller is positioned upward, and fog is reduced. Therefore, the developer overflow portion before the developing nip comes into contact with the photosensitive member by gravity. It is considered that the charging is facilitated and charging is promoted.

(Embodiment 4)
In the developing device according to the first embodiment, the developing sleeve 26M rotates in the width direction with respect to the rotation direction of the photosensitive drum 1M at a peripheral speed of 120 mm / s, and a peripheral speed ratio of 1.2 with respect to the photosensitive drum 1M. However, the peripheral speed of the developing sleeve was changed to 1.1 to 3.5. At the time of initial adjustment, the fog was 0.7 to 0.9% under the respective conditions, the image density was 1.5 ± 0.02, and the charge amount was −25.8 ± 1.1 μC / g. Further, the fog and image density and charge amount after continuously printing 10 solid images continuously in the initial stage, and the fog and image density after continuously printing 10 sheets after printing 30,000 sheets. The results of the charge amount test are shown in Table 4. It was confirmed that good results were initially obtained for fog at a peripheral speed ratio of 1.3 or more and 3.5 or less, and the charge amount was also increased. Furthermore, a print test of 30,000 sheets was carried out with this good peripheral speed ratio of 1.3 to 3.5. A high charge amount was maintained after printing 30,000 sheets at a peripheral speed ratio of 1.3 to 3.0, fog was small, and image density was stable. By providing the peripheral speed ratio between the photosensitive member and the developing sleeve, toner charging is promoted and fog is reduced. Therefore, the overflow of the developer before the developing nip is disturbed by the peripheral speed difference, and the developer charging is promoted. It is considered a thing.

  On the other hand, when the peripheral speed ratio exceeds 3.0, the amount of charge is reduced, causing problems of increased fog and increased image density. This is considered to be caused by so-called developer deterioration in which pressure is applied to the developer and an external additive or the like adheres to the carrier.

(Embodiment 5)
In the developing device according to the first embodiment, the experiment was performed by changing the conditions from −2 degrees to 13 degrees with respect to the main pole magnetic pole angle of 0 degrees. At the time of initial adjustment, the fog was 0.7 to 0.8% under the respective conditions, the image density was 1.5 ± 0.02, and the charge amount was −25.7 ± 0.8 μC / g. Further, fog and image density and charge amount after continuously printing 10 solid images continuously in the initial stage, and fog and image density after continuously printing 10 sheets after printing 30,000 sheets. The results of the charge amount test are shown in Table 5.

  When the main pole magnetic pole angle is in the range of 1 to 10 degrees, it was confirmed that initially good results were obtained with respect to fog and that the charge amount was higher than that of the main pole angle of 0 degrees. Further, 30,000 printing tests were performed on the condition of this good main pole magnetic pole angle of 1 to 10 degrees. Even after printing 30,000 sheets, a high charge amount was maintained, fog was small, and image density was stable. By positioning the magnetic pole center of the main pole on the downstream side of the sleeve rotation, it is considered that a larger developer pool can be formed and toner charging is promoted.

(Embodiment 6)
As shown in FIG. 5, in the developing device in the first embodiment, a fixed magnet M51 having a surface magnetic force of 60 mT is included inside the photoconductor. The peak position of the magnetic force was set at a position moved about 3 degrees upstream of the development nip. At the time of initial adjustment, the fog was 0.7 to 0.9% under the respective conditions, the image density was 1.5 ± 0.02, and the charge amount was −25.4 ± 1.0 μC / g. Further, fog and image density and charge amount after continuously printing 10 solid images continuously in the initial stage, and fog and image density after continuously printing 10 sheets after printing 30,000 sheets. The results of the charge amount test are shown in Table 6. By using a photoconductor including a magnet, it was confirmed that a good result with respect to fog was initially obtained and the amount of charge was high as compared with the first embodiment. Further, when a printing test of 30,000 sheets was performed, a high charge amount was maintained after printing 30,000 sheets, fog was small, and the image density was stable. It is considered that inclusion of a magnet inside the photosensitive member can form a larger developer reservoir and promote toner charging.

(Embodiment 7)
A carrier coated with a fluorine-modified silicone resin and a fluorine-modified acrylic resin was prepared for the carrier coated with the dimethyl silicone resin in the first embodiment. Volume resistivity 1.8 × 10 ¹⁰ Ω · cm, specific gravity 5.0 g / cm ³ , magnetization 61.9 Am ² / kg, volume resistivity 2.1 × 10 ¹⁰ Ω · cm, specific gravity 5.0 g / cm ^3. Two types of carriers having a magnetization of 61.9 Am ² / kg were prepared. At the time of initial adjustment, the fog was 0.7 to 0.8% under the respective conditions, the image density was 1.5 ± 0.02, and the charge amount was −26.0 ± 1.0 μC / g. Further, fog and image density and charge amount after continuously printing 10 solid images continuously in the initial stage, and fog and image density after continuously printing 10 sheets after printing 30,000 sheets. The results of the charge amount test are shown in Table 7.

  By using a fluorine-modified silicone resin and a fluorine-acrylic-modified resin, it was confirmed that a favorable result was initially obtained with respect to fog and that the charge amount was also higher than in the first embodiment. . Further, when a printing test of 30,000 sheets was performed, a high charge amount was maintained after printing 30,000 sheets, fog was small, and the image density was stable. By using a carrier having high surface releasability, it is considered that the movement of the developer in the developer reservoir is improved and the charging of the toner is promoted.

(Embodiment 8)
A toner having an SF1 value of 101 to 160 was prepared while changing the aggregation conditions with respect to the toner of the emulsion polymerization aggregation method of the first embodiment.

  At the time of initial adjustment, the fog was 0.6 to 0.9% under the respective conditions, the image density was 1.5 ± 0.03, and the charge amount was −26.0 ± 1.5 μC / g. Further, fog and image density and charge amount after continuously printing 10 solid images continuously in the initial stage, and fog and image density after continuously printing 10 sheets after printing 30,000 sheets. The results of the charge amount test are shown in (Table 8).

  By setting the SF1 value to 150 or less, it was confirmed that, compared to the first embodiment, an initial favorable result for fogging was obtained and the charge amount was also increased. Further, when a printing test of 30,000 sheets was performed, a high charge amount was maintained after printing 30,000 sheets, fog was small, and the image density was stable. By using the spherical toner, it is considered that the toner acts as a roller, and the movement of the developer in the developer reservoir is improved, and the charging of the toner is promoted.

  In the present invention, the emulsion polymerization method is used to obtain 101 to 160 as the spheroidization degree SF1 value. However, the spheroidization can be performed by a suspension polymerization method, a method of performing heat treatment after pulverization, or the like as necessary. .

  The vertical circulation developing apparatus of the present invention can be applied to electrophotographic image forming apparatuses such as copying machines, facsimiles, and laser printers.

FIG. 1 is a cross-sectional view of a main part showing an outline of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view of the main part showing an outline of the image forming unit according to the first embodiment of the present invention. 1 is a perspective view schematically showing a developing device according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view of the main part of the developing device shown in FIG. Sectional drawing which shows the outline of the image forming unit in Embodiment 5 of this invention

Explanation of symbols

1M photosensitive drum 4M developing roller 8M developing device 13M partition wall 14M first developer transport path 15M second developer transport path 16M overhang 17M second transport screw 19M first transport screw 23M toner concentration sensor 24M toner supply port 25M ear Cutting shaft 26M Development sleeve

Claims (7)

Toner prepared by emulsion polymerization aggregation method, or toner having a charge control agent content of 1 wt% or less, developer composed of carrier, and electrostatic latent image holding capable of rotating by forming an electrostatic latent image on the surface A developer carrying body having a body and a plurality of magnetic field generating means, and holding a magnetic brush formed from the developer to visualize the electrostatic latent image and contacting the electrostatic latent image holding body And
M / L when the total weight of the developer in the apparatus is M (g) and the axial length carrying the developer on the developer carrier is L (cm). Is 3 g / cm or more and 9 g / cm or less, the closest distance DSD between the electrostatic latent image holding body and the developer carrying body is d (mm), and the electrostatic latent image holding body is The development satisfying the relationship of 2 ≦ h / d ≦ 3.5, where h (mm) is the average ear height of the magnetic brush on the developer carrier in a state where they are not opposed to each other. apparatus. The developer carrying body is positioned above the electrostatic latent image holding body, and the angle between the line connecting the electrostatic latent image holding body and the center of the developer carrying body and the horizontal line is 30 degrees or more and 150 degrees or less. The developing device according to claim 1, wherein the developing device is within the scope of the claims. The peripheral speed ratio of the developer carrier relative to the electrostatic latent image carrier is 1.3 times or more and 3.0 times or less. The developing device described. The main pole peak position of the developer carrying member is not less than 1 degree and not more than 10 degrees on the upstream side from the position facing the electrostatic latent image holding body. 4. The developing device according to any one of items 3 to 3. The magnetic field generating means for attracting the developer of the magnetic brush is provided at least in the vicinity of the developer carrying body inside the electrostatic latent image holding body. The developing device according to 1. The developing device according to any one of claims 1 to 5, wherein at least a fluorine-modified silicone resin or a fluorine-modified acrylic resin is provided on a surface of the resin carrier. At least an electrostatic latent image holding member capable of rotating by forming an electrostatic latent image on the surface;
In order to visualize the electrostatic latent image, when the powder projection area is A, the absolute maximum length of the powder is M, and the shape factor (SF-1) of the powder is expressed by (Equation 1), The developing device according to any one of claims 1 to 6, wherein a toner having a shape factor (SF-1) of 100 or more and 150 or less is used.

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