JP2009122284A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the generation of fog caused by the development of toner having deteriorated charging characteristics on a non-image area. <P>SOLUTION: After power is turned on and before a development operation of an electrostatic latent image with a developing device 19 is started, a developing bias lower than a developing bias applied in the development operation is applied. While applying the developing bias, a preprocessing operation to work a photoreceptor drum 16 and the developing device 19 for a predetermined time is performed. By the preprocessing operation, faultily charged toner which causes fogging, such as toner having a reduced charge amount and toner charged to the reverse polarity is deposited on a surface of the photoreceptor drum and removed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine and a printer.

  In general, an image forming apparatus using an electrophotographic system forms an image through the steps of charging, exposure, development, transfer, peeling, cleaning, static elimination, and fixing. In the step of forming an image, for example, the surface of the photoconductor to be rotated is uniformly charged by a charging device, and the surface of the photoconductor charged by the exposure device is irradiated with laser light to form an electrostatic latent image. Subsequently, the electrostatic latent image on the photoconductor is developed by the developing device, and a toner image is formed on the surface of the photoconductor. The toner image on the photosensitive member is transferred onto the transfer material by the transfer device, and then heated by the fixing device, whereby the toner image is fixed on the transfer material. Further, the transfer residual toner remaining on the surface of the photoreceptor is removed by a cleaning device and collected in a predetermined collection unit. In addition, the remaining charge is removed from the surface of the photoreceptor after the cleaning by a static eliminator in order to prepare for the next image formation.

  As the developer for developing the electrostatic latent image on the photoreceptor, a one-component developer composed of only toner or a two-component developer composed of toner and carrier is generally used.

  Since the one-component developer does not use a carrier, a stirring mechanism or the like for uniformly mixing the toner and the carrier is not required unlike the two-component developer. Therefore, there is an advantage that the developing device is simplified. However, there are drawbacks such as the toner charge amount being difficult to stabilize.

  Since the two-component developer requires a stirring mechanism for uniformly mixing the toner and the carrier, there is a disadvantage that the developing device becomes complicated. However, it has excellent charging stability and compatibility with high-speed machines. Therefore, it is often used in high-speed image forming apparatuses and color image forming apparatuses.

  As the toner used in the two-component developer, resin particles in which an external additive for imparting fluidity is added to the surface of the resin particles containing a colorant having a particle diameter of 5 to 8 μm dispersed therein are used. . As the carrier used for the two-component developer, magnetic particles made of ferrite or the like having a particle diameter of 20 to 100 μm are used. The magnetic particles are coated with an acrylic resin or silicone resin containing a conductive material such as carbon black on the surface of the magnetic particles as core particles in order to prevent humidity dependency and toner component fusion. Coating carriers with a layer are known.

  Furthermore, Patent Document 1 discloses a coating carrier having two coating layers so that the carrier is agitated in the developing tank and the coating layer is worn away so that the resistance and charge imparting ability of the carrier do not change with time. Is disclosed.

JP 2001-92190 A

  However, even with a two-component developer using a carrier having two coating layers, if the developer is stirred for a long time in the developing device, the external additive is buried from the resin particle surface to the inside, and the fluidity of the toner Will fall. Such toners have a low spacer effect due to external additives, and the charge amount of the toner is likely to be lowered by leaving it for a long time (standing), or the charge rising property by stirring is poor, and the charging characteristics are greatly improved. Will deteriorate. The toner having a deteriorated charging characteristic is easily attached to the non-image area and is developed as a fog toner.

  An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of fog caused by developing such a toner having deteriorated charging characteristics in a non-image area.

The present invention relates to a photosensitive drum, a charging device for charging the surface of the photosensitive drum to a specified potential, an exposure device for forming an electrostatic latent image on the photosensitive drum charged by the charging device, a toner and a carrier. In an image forming apparatus comprising: a developing device that contains the two-component developer, and developing the electrostatic latent image; and a developing bias supply unit that applies a developing bias to the developing device.
After the power is turned on and before starting the developing operation by the developing device, a pre-processing operation for operating the photosensitive drum and the developing device for a predetermined time while applying a developing bias value lower than the developing bias value applied in the developing operation is performed. An image forming apparatus characterized by the above.

  In the invention, it is preferable that the preprocessing operation is performed so that the toner density ID on the surface of the photosensitive drum is 0.5 or less.

  In the pre-processing operation, the present invention is characterized in that the developing bias potential is applied for 5 seconds to 60 seconds.

  In the pretreatment operation, the potential difference between the surface potential of the photosensitive drum and the developing bias potential is less than ± 100V.

  In the invention, it is preferable that the toner includes an external additive having a number average particle diameter of 80 nm to 300 nm.

In the invention, it is preferable that the carrier is a coating carrier coated with a thermosetting silicone resin.
In the invention, it is preferable that the core particle is composed of a ferrite component.

  According to the present invention, after the power is turned on and before the developing operation by the developing device is started, the photosensitive drum and the developing device are operated for a predetermined time while applying a developing bias value lower than the developing bias value applied in the developing operation. Perform pre-processing operations.

  By performing such a pre-processing operation, poorly charged toner that causes fogging, such as toner having a reduced charge amount or charged toner having a reverse polarity, is selectively attached to the surface of the photosensitive drum before the development operation is started. As a result, it is possible to suppress the occurrence of fog caused by removing the poorly charged toner and developing it in the non-image area.

  Further, according to the present invention, the preprocessing operation is performed so that the toner density ID on the surface of the photosensitive drum is 0.5 or less, so that even a normally charged toner is not removed, and the toner consumption is reduced. Can be reduced.

  According to the invention, in the pre-processing operation, the developing bias potential is applied for 5 seconds or more and 60 seconds or less.

  Accordingly, it is possible to effectively remove the poorly charged toner from the two-component developer while preventing unnecessary stirring.

  According to the invention, in the pre-processing operation, the potential difference between the surface potential of the photosensitive drum and the developing bias potential is less than ± 100V.

  Accordingly, it is possible to effectively remove the poorly charged toner from the two-component developer while suppressing consumption of the normally charged toner.

  According to the invention, the toner includes an external additive having a number average particle diameter of 80 nm to 300 nm.

  Thereby, since the embedding of the external additive on the surface of the toner (colored resin particles) can be delayed, the amount of toner removed and consumed by the pretreatment operation can be reduced.

  According to the invention, the carrier is a coated carrier coated with a thermosetting silicone resin.

  As a result, the carrier surface is coated with a hard resin and the external additive can be prevented from being buried in the carrier surface, so that the carrier can maintain a stable chargeability for a long period of time, and the occurrence of poorly charged toner can be suppressed.

  According to the invention, since the core particles are composed of a ferrite component, a carrier having a low specific gravity can be obtained, and the stirring torque when stirring the two-component developer can be reduced. As a result, the embedding of the external additive on the toner particle surface is delayed, and the occurrence of poorly charged toner can be reduced.

The image forming apparatus of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing an entire image forming apparatus 100 according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a main part of the image forming apparatus 1.

  As shown in FIG. 1, the image forming apparatus is a tandem color image forming apparatus including four image forming units 1 to 4. The first image forming unit 1 is a unit that forms a black toner image, the second image forming unit 2 is a unit that forms a cyan toner image, and the third image forming unit 1 forms a magenta toner image. The fourth image forming unit 4 is a unit that forms a yellow toner image.

  Above these four image forming units 1 to 4, an intermediate transfer belt (endless belt) 5 is disposed. The intermediate transfer belt 5 is stretched over two support rolls 6a and 6b and is configured to rotate in the direction indicated by the arrow R. Hereinafter, with respect to the rotation direction R of the intermediate transfer belt 5, the upstream and downstream of the rotation direction are defined with reference to the secondary transfer position where the secondary transfer roller 8 is disposed. As a material for the intermediate transfer belt 5, a material in which an appropriate amount of an electron conductive material is contained in a resin such as polyimide or polyamide can be used.

  The four image forming units 1 to 4 are, from the upstream side in the rotation direction R of the intermediate transfer belt 5, the first image forming unit 1 (black), the second image forming unit 2 (cyan), and the third image forming unit 3. (Magenta) and fourth image forming unit 4 (yellow) are arranged in this order.

  Inside the intermediate transfer belt 5, a primary transfer roller 7 that transfers the single-color toner image formed by the image forming units 1 to 4 onto the intermediate transfer belt 5 faces the image forming units 1 to 4. Are provided respectively. The single color toner images formed by the respective image forming units 1 to 4 are transferred so as to be superimposed on the intermediate transfer belt 5 to form one color toner image.

  Secondary transfer for transferring the color toner image formed on the intermediate transfer belt 5 to a sheet (recording medium) downstream of the fourth image forming unit 4 (yellow) in the rotation direction R of the intermediate transfer belt 5. A roller 8 is provided.

  Further, a belt cleaning unit 10 for cleaning the surface of the intermediate transfer belt 5 after transfer is provided downstream of the secondary transfer roller 8 in the rotational direction R of the intermediate transfer belt 5. The belt cleaning unit 10 includes a belt cleaning brush 11 disposed in contact with the intermediate transfer belt 5 and a belt cleaning blade 12. The belt cleaning blade 12 is disposed downstream of the belt cleaning brush 11 in the rotation direction R of the intermediate transfer belt 5.

  Further, below the four image forming units 1 to 4, a tray 14 for storing paper is disposed. The paper in the tray 14 is conveyed to a secondary transfer position where the secondary transfer roller 8 faces the intermediate transfer belt 5 by a plurality of paper feed rollers 13. An arrow P indicates a conveyance direction of the sheet from the tray 14 to the secondary transfer roller 8.

  A fixing unit 15 for fixing the color toner image transferred onto the paper on the paper is provided downstream of the secondary transfer roller 8 in the paper conveyance direction. Further, on the further downstream side in the transport direction P of the fixing unit 15, a paper discharge roller 13 a that discharges the paper on which the color toner image has been fixed by the fixing unit 15 from the image forming apparatus 100 is provided.

  In such a configuration, the single color toner images formed by the image forming units 1 to 4 are sequentially transferred onto the intermediate transfer belt 5 to form a color toner image on the intermediate transfer belt 5. The color toner image on the intermediate transfer belt 5 is secondarily transferred onto the paper conveyed by the paper feed roller 13 at the secondary transfer position, and then fixed on the paper by the fixing unit 15. The sheet on which the color image is fixed is discharged from the image forming apparatus by the discharge roller 13a. On the other hand, after the secondary transfer, the toner remaining on the intermediate transfer belt 5 without being transferred to the paper is removed by the belt cleaning unit 10.

  FIG. 2 shows only the first image forming unit 1 shown in FIG. The configurations of the second image forming unit 2, the third image forming unit 3, and the fourth image forming unit 4 are substantially the same as those of the first image forming unit 1. Detailed descriptions of the configurations of the image forming unit 3 and the fourth image forming unit 4 are omitted.

  As shown in FIG. 2, an electrostatic latent image is written on the photosensitive drum 16 and the charging device 17 that charges the photosensitive drum 16 around the photosensitive drum 16 provided in the image forming apparatus 100 of the present embodiment. Exposure device 18, developing device 19 that visualizes an electrostatic latent image on photoconductor drum 16, fog density sensor 26, cleaning device 20 that removes a residue including toner remaining on photoconductor drum 16, and photoconductor drum The static elimination lamp 25 for removing the upper residual charge is arranged in this order along the rotation direction Rd of the photosensitive drum 16.

  The charging device 17 includes a scorotron charging device, and includes a control grid (control grid) 17b capable of controlling the amount of corona ions reaching the surface of the photosensitive drum 16 from the saw-tooth electrode (discharge electrode) 17a. A high voltage power source (not shown) that outputs a high voltage of several kV is connected to the saw-tooth electrode 17a. The control grid 17b includes a high voltage power source 32 having a high voltage transformer (TH) and a low voltage power source 33 having a constant voltage power source and having a low voltage transformer (TL) via a changeover switch 31. Is connected. In the present embodiment, the output voltage of the low voltage power supply 33 is about 200V, and the output voltage of the high voltage power supply 32 is about 650V. However, the polarity of the voltage is negative. The changeover operation of the changeover switch 31 is controlled by a control device 34 having a microcomputer, for example.

  The exposure device 18 is composed of, for example, a laser exposure device, performs exposure by laser scanning in accordance with an input image signal, and changes the surface potential of the photosensitive drum 16 charged by the charging device 17, thereby changing the image information. A corresponding electrostatic latent image is formed. An LDE array device or the like can also be used as the exposure device.

  The developing device 19 contains a developing roller 24 that contains therein a two-component developer composed of a carrier and toner (in this embodiment, negatively charged toner is used) and supplies the two-component developer to the surface of the photosensitive drum 16. I have. The two-component developer contains a magnetic carrier and toner, and develops the electrostatic latent image formed on the photosensitive drum 16 by a two-component reversal development method. The fog density sensor 26 is a sensor that measures the toner adhesion amount on the non-image portion on the surface of the photosensitive drum 16, and is composed of a photosensor including a light emitting element and a light receiving element, and outputs a measurement result to the control device 34.

  The toner image developed by the developing device 19 is primarily transferred onto the intermediate transfer belt 5. The toner remaining on the surface of the photoconductive drum 16 after the transfer is collected by the cleaning device 20, while the charge remaining on the surface of the photoconductive drum 16 is removed by the charge eliminating lamp 25.

  The image forming operation in the image forming apparatus 100 is performed as follows. First, the photosensitive drum 16 is rotationally driven by a drum motor, and the surface of the photosensitive drum 16 is charged to a uniform potential by the charging device 17. Next, the surface of the photosensitive drum 16 is irradiated with laser light from the exposure device 18 to form an electrostatic latent image. The electrostatic latent image is formed on the photosensitive drum 16 by an aluminum base tube (not shown) that forms the base of the photosensitive drum 16 connected to the ground from the drum flange via the drum shaft. This is performed by lowering the potential of the exposed portion as compared to the unexposed portion.

  The formed electrostatic latent image is developed with the charged toner supplied from the developing device 19 and becomes a toner image. At this time, a developing bias is applied to the developing roller 24 of the developing device 19 from a developing bias power source 35 in order to supply toner to the surface of the photosensitive drum 16. In the present embodiment, the output voltage on the plus side is 150V, and the output voltage on the minus side is 100V and 500V. However, the output voltage is controlled by, for example, a control device 34 including a microcomputer.

  FIG. 3 is a timing chart showing the operation timing and application timing of the drum motor, control grid voltage, and developing bias.

  Each part operates at the timing shown in FIG. 3 from the start of rotation of the drum motor until the surface potential of the photosensitive drum rises to the specified potential. At time t1, the drum motor starts rotating, and at the same time, the charging device 17 supplies a high voltage to the saw-tooth electrode 17a, and the changeover switch 31 is switched to the low voltage power source 33 side, thereby controlling the control grid 17b. A predetermined low grid voltage (−200 V) is supplied from the low voltage power supply 33. Although not shown in FIG. 3, the static elimination lamp 25 is turned on simultaneously. In addition, in the developing device 19, a predetermined positive developing bias voltage (+150 V) is supplied from the developing bias supply means 35 to the developing roller 24 at time t 1.

  Next, at time t2, in the charging device 17, the changeover switch 31 is switched to the high voltage power supply 32 side, and a predetermined high grid voltage (−650 V) is supplied to the control grid 17b. At this time, the applied grid voltage is increased by about −40 V by dividing the low voltage (−200 V) to the high voltage (−650 V) into 8 steps. By increasing the grid voltage in a plurality of stages, it is possible to prevent the occurrence of unstable portions of the photosensitive drum surface potential when rising, and to linearly raise the surface potential of the photosensitive drum to a specified potential. As a result, it is possible to prevent deterioration of the photosensitive drum due to scattering of the carrier, deterioration of image quality due to toner aggregation caused by scattering carrier at the time of toner recycling, and adhesion of reversely charged toner to the photosensitive drum and increase in toner consumption. In addition, an image with stable image quality can be obtained.

  On the other hand, at time t3 after a predetermined time a from time t1, the developing device 19 is supplied with a negative low developing bias voltage (−200 V) to the developing roller 24, and is negative at time t4 after a predetermined time b from time t3. Side high development bias voltage (-500V) is supplied.

  If the developing bias remains at 0 V during the period until the photosensitive drum 16 starts rotating and the portion where the surface potential of the photosensitive drum 16 increases due to the application of the grid voltage to the control grid 17b reaches the developing portion, the development is continued. Since the surface potential of the photosensitive drum in the portion passing through the portion is 0 V, the toner adheres to the portion passing through the developing portion. Further, when a voltage having the same polarity as the grid voltage is applied as a developing bias at this time, toner adheres to the surface of the photosensitive drum 16 regardless of the amount of charge of the toner. In the period up to reaching, by applying a developing bias having a polarity opposite to the grid voltage to the developing device 19, it is possible to prevent the toner from adhering to the surface of the photosensitive drum 16. As a result, an increase in toner consumption can be prevented and an image with stable image quality can be obtained.

  The switching timing from the low voltage power source 33 side to the high voltage power source 32 side by the changeover switch 31 is immediately after the surface potential of the photosensitive drum 16 rises after the low voltage power source 33 is applied to the control grid 17b (about 0.2 seconds). Later). When the potential is supplied from the charging device 17 as described above, the surface potential of the photosensitive drum 16 rises and finally becomes a specified potential. At this time, a low voltage bias is first applied from the low voltage power supply 33 to the control grid 17b of the charging device 17, and then a high voltage is applied from the high voltage power supply 32. The rise of is as shown in FIG.

  FIG. 4 is a graph showing the rise of the surface potential of the photosensitive drum 16. The horizontal axis indicates elapsed time (sec), and the vertical axis indicates potential (V).

  The elapsed time is 0 at the time t1 shown in FIG. 3, that is, the rotation start time of the drum motor. The surface potential of the photosensitive drum 16 increases stepwise from 0V with the output of the control grid voltage, and reaches a specified potential (−600V).

  In the image forming apparatus of the present invention, after the power is turned on, gray development is performed prior to the normal image forming operation described above.

  In the present invention, gray development is a state in which no electrostatic latent image is formed, and the potential difference between the surface potential of the photosensitive drum 16 and the developing bias potential is less than ± 100 V, and the photosensitive drum 16 and the developing roller 24 Is an operation of attaching a toner having a predetermined density or less to the surface of the photosensitive drum 16 by rotating the image forming apparatus. After the image forming apparatus has been stopped for a long time, the toner having a reduced charge amount, the reverse polarity This is an operation in which poorly charged toner that causes fogging, such as a charged toner, is attached to the photosensitive drum 16 in advance and removed. As the predetermined toner density, for example, the ID is about 0.5.

  FIG. 5 is a timing chart showing the operation timing and application timing of the drum motor, the control grid voltage, and the developing bias during gray development.

  The drum motor starts rotating at time tx, and a developing bias potential of −10 V is applied from time tx to time ty after a predetermined time (for example, 30 seconds) has elapsed. At this time, the control grid voltage is not applied to the saw-tooth electrode 17a and the control grid 17b.

  Here, time tx and time ty are both times prior to time t1. That is, the gray development is a preprocessing operation performed before the development operation for developing the electrostatic latent image is started.

  When the control grid voltage is applied, the developing bias potential is applied so that the potential difference between the surface potential of the photosensitive drum 16 and the developing bias potential is −50V to + 50V. The application time is preferably 5 seconds to 60 seconds, and particularly preferably 5 seconds to 30 seconds. If the application time is shorter than 5 seconds, the poorly charged toner that causes fogging is not sufficiently removed by the gray development, and if the applied time exceeds 60 seconds, the toner other than the toner with defective charge amount is developed. End up.

  When the development bias potential is larger than −100 V on the minus side, not only the poorly charged toner but also the toner having a normal charge amount is easily removed by the gray development, and excess toner is consumed. On the contrary, if the developing bias potential is larger than + 100V on the plus side, the poorly charged toner is not removed by gray development.

  Note that the gray development for consuming the poorly charged toner is performed not only after the power is turned on, but also after the lapse of a certain time with the toner still in the developing tank even when the power is turned on. Also good.

Next, a two-component developer that can be used in the image forming apparatus of the present invention will be described.
The two-component developer can be prepared by mixing the toner and the carrier. Generally, the two-component developer can be prepared by mixing 3 to 15 parts by weight of the toner with respect to 100 parts by weight of the carrier and stirring the mixture with a mixer such as a Nauta mixer. .

  The toner is not particularly limited, and any known toner can be used. For example, the toner described below can be used.

  The toner includes colored resin particles (toner particles) and, if necessary, external additives attached to the surface of the colored resin particles. The external additive is preferably contained in the toner from the viewpoint of preventing the toner from agglomerating and preventing the transfer efficiency when transferring from the photosensitive drum to the recording medium.

  The toner can be produced, for example, by mixing the external additive with the colored resin particles using an air flow mixer such as a Henschel mixer (that is, external addition treatment). The volume average particle diameter of the colored resin particles is preferably in the range of 4 to 7 μm. Within this range, a high-quality image with excellent dot reproducibility and less fog and toner scattering can be obtained. The definition of the volume average particle diameter is described below.

The BET specific surface area of the colored resin particles is preferably 1.5 to 1.9 m ² / g. When the BET specific surface area exceeds 1.9 m ² / g, the colored resin particle surface is uneven, and the external additive may enter the concave portion, and the external additive may not be uniformly adhered to the surface. In this case, the roller effect (effect of improving fluidity) and the spacer effect (preventing charge leakage) of the external additive cannot be sufficiently obtained, and fog and toner scattering are likely to occur. Moreover, if it is less than 1.5 m < ² > / g, the colored resin particle surface may become smooth too much, and fogging may generate | occur | produce when cleaning defect generate | occur | produces.

  A known method can be used as a method for controlling the BET specific surface area. For example, there are a method such as a method in which colored resin particles are rotated in a cylindrical pipe at a high speed to make a corner, and a method such as a sfufusion system that instantaneously melts toner in a hot air stream. The definition of the BET specific surface area is described below.

  The colored resin particles can be produced by a known method such as a kneading and pulverizing method or a polymerization method. Specifically, when the kneading and pulverization method is adopted, the binder resin, the colorant, the charge control agent, the release agent, and other additives are mixed with a mixer such as a Henschel mixer, a super mixer, a mechano mill, or a Q type mixer. Mix. The obtained raw material mixture is melt-kneaded at a temperature of about 100 to 180 ° C. by a kneader such as a twin-screw kneader or a single-screw kneader. The obtained kneaded product is cooled and solidified, and the solidified product is pulverized by an air pulverizer such as a jet mill. Colored resin particles can be produced by adjusting the particle size such as classification of the obtained pulverized product as necessary.

  As the binder resin that can be used for the toner, various known styrene resins, acrylic resins, polyester resins, and the like can be used. A linear or non-linear polyester resin is particularly preferable. The polyester resin is excellent in achieving both mechanical strength (difficult to generate fine powder), fixability (hard to peel off from paper after fixing), and hot offset resistance.

  The polyester resin can be obtained by polymerizing a monomer composition composed of a polyhydric alcohol having two or more valences and a polybasic acid. Examples of the divalent alcohol used for polymerization of the polyester resin include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1 Diols such as 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, bisphenol A alkylene such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A Examples thereof include oxide adducts and the like.

  Examples of the divalent polybasic acid include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, Examples include malonic acid, anhydrides and lower alkyl esters of these acids, or alkenyl succinic acids or alkyl succinic acids such as n-dodecenyl succinic acid and n-dodecyl succinic acid.

  If necessary, a trihydric or higher polyhydric alcohol or a polybasic acid may be added to the monomer composition. Examples of the trihydric or higher polyhydric alcohol include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose, 1,2,4- Butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethyl Benzene and others can be mentioned.

  Examples of the tribasic or higher polybasic acid include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 2,5,7-naphthalenetricarboxylic acid. 1,2,4-naphthalenetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra (methylenecarboxyl) methane, 1,2,7 , 8-octanetetracarboxylic acid, and anhydrides thereof.

  As the colorant that can be used in the toner, known pigments and dyes generally used in toners can be used.

  Specific examples of the black toner include carbon black and magnetite.

  For yellow toner, C.I. I. Pigment Yellow 1, 3, 74, 97, 98, etc. acetoacetic acid arylamide monoazo yellow pigments, C.I. I. Pigment Yellow 12, 13, 13, 14, etc., acetoacetic acid arylamide disazo yellow pigments, C.I. I. Condensed monoazo yellow pigments such as CI Pigment Yellow 93 and 155; I. Other yellow pigments such as C.I. Pigment Yellow 180, 150 and 185, C.I. I. Solvent Yellow 19, 77, 79, C.I. I. Examples include yellow dyes such as Disperse Yellow 164.

  For magenta toner, C.I. I. Pigment Red 48, 49: 1, 53: 1, 57, 57: 1, 81, 122, 5, 146, 184, 238; I. Red or red pigments such as CI Pigment Violet 19; I. Examples thereof include red dyes such as Solvent Red 49, 52, 58 and 8.

  For cyan toner, C.I. I. Pigment Blue 15: 3, 15: 4, and the like, and blue dyes and pigments of copper phthalocyanine and derivatives thereof; C.I. I. Examples thereof include green pigments such as CI Pigment Green 7 and 36 (phthalocyanine green).

  As content of a coloring agent, it is preferable that it is about 1-15 weight part with respect to 100 weight part of binder resin, More preferably, it is the range of 2-10 weight part.

As the charge control agent that can be used for the toner, known charge control agents can be used.
Specifically, as a charge control agent imparting negative chargeability, chromium azo complex dye, iron azo complex dye, cobalt azo complex dye, salicylic acid or its derivative chromium / zinc / aluminum / boron complex or salt compound, naphtholic acid or Chromium / zinc / aluminum / boron complex or salt compound of its derivative, chrome / zinc / aluminum / boron complex or salt compound of benzylic acid or its derivative, long chain alkyl / carboxylate, long chain alkyl / sulfonate, etc. Can be mentioned.

  Examples of the charge control agent that imparts positive chargeability include nigrosine dyes and derivatives thereof, triphenylmethane derivatives, quaternary ammonium salts, quaternary phosphonium salts, quaternary pyridinium salts, guanidine salts, amidine salts, and the like. be able to.

  The content of these charge control agents is preferably in the range of 0.1 to 20 parts by weight, more preferably in the range of 0.5 to 10 parts by weight with respect to 100 parts by weight of the binder resin. .

  Release agents that can be used for the toner include synthetic waxes such as polypropylene and polyethylene, paraffin wax and derivatives thereof, petroleum waxes such as microcrystalline wax and derivatives thereof, and modified waxes thereof, carnauba wax, rice wax, and candelilla wax. And plant waxes. By including these release agents in the toner, the releasability of the toner with respect to the fixing roller or the fixing belt can be improved, and high temperature / low temperature offset during fixing can be prevented. The amount of the release agent added is not particularly limited, but is generally 1 to 5 parts by weight with respect to 100 parts by weight of the binder resin.

  As the external additive, inorganic particles made of silica, titanium oxide, alumina or the like having an average particle diameter of 7 nm to 100 nm can be used. Moreover, you may provide hydrophobicity by surface-treating an inorganic particle with a silane coupling agent, a titanium coupling agent, and silicone oil. Inorganic particles to which hydrophobicity is imparted are preferable because the decrease in electrical resistance and charge amount is reduced under high humidity. In particular, silica particles using hexamethyldisilazane (hereinafter sometimes referred to as HMDS) as a silane coupling agent and having a trimethylsilyl group introduced on the surface are excellent in hydrophobicity and insulating properties. The toner to which the silica particles are externally added can provide excellent chargeability even in a high humidity environment.

  Specific external additives include Aerosil 50 (number average particle size: about 30 nm), Aerosil 90 (number average particle size: about 30 nm), Aerosil 130 (number average particle size: about 16 nm) manufactured by Nippon Aerosil Co., Ltd. Aerosil 200 (number average particle size: about 12 nm), Aerosil 300 (number average particle size: about 7 nm), Aerosil 380 (number average particle size: about 7 nm), Aluminum Oxide C (number average particle size: manufactured by West Germany Degussa) About 13 nm), titanium oxide P-25 (number average particle size: about 21 nm), MOX170 (number average particle size: about 15 nm), Ishihara Sangyo TTO-51 (number average particle size: about 20 nm), TTO-55 (Number average particle diameter: about 40 nm).

  As the external additive, it is easy to be embedded in the toner surface when the particle size becomes small. Therefore, it is desirable to add an external additive having a number average particle size of 80 nm or more in addition to the external additive. When the particle diameter exceeds 300 nm, the toner particles are detached from the toner surface and accumulate in the lower part of the developing tank. Therefore, an external additive having a number average particle diameter of 80 nm to 300 nm is preferable.

  The amount of the external additive added is preferably 0.2 to 3% by weight. If it is less than 0.2% by weight, the toner may not be sufficiently or fluidly provided. On the other hand, if it exceeds 3% by weight, the toner fixability may be lowered.

  The carrier of the present invention has core particles, a first coating layer that coats the core particles, and a second coating layer that coats the outside of the first coating layer, and the first coating layer and the second coating layer are respectively The resin and the conductive material are included, and the second coating layer contains the conductive material at a higher content than the first coating layer. According to the carrier of the present invention, when the charge amount of the toner immediately after the start and the wear of the coating resin progress (when the convex part of the core particle is exposed), the carrier to the photoreceptor due to the significant decrease in the carrier resistance. Adhesion and image roughness can be prevented.

  The carrier that can be used in the present invention is not particularly limited, but the volume average particle diameter is preferably 20 to 100 μm. If the volume average particle diameter is too small, white spots may occur in the resulting image due to the carrier moving from the developing roller to the photosensitive drum during development. On the other hand, if the size is too large, the dot reproducibility may deteriorate and the image may become rough. The volume average particle diameter is more preferably 30 to 60 μm. Here, the volume average particle size means the total particle size of the core particles, the first coating layer, and the second coating layer, and a specific definition of the volume average particle size is described below.

  The lower the saturation magnetization of the carrier, the softer the magnetic brush in contact with the photosensitive drum, so that an image faithful to the electrostatic latent image can be obtained. However, if the saturation magnetization is too low, carriers adhere to the surface of the photosensitive drum and white spots are likely to occur. On the other hand, if the saturation magnetization is too high, it becomes difficult to obtain an image faithful to the electrostatic latent image due to the stiffening of the magnetic brush. Therefore, the saturation magnetization of the carrier is preferably in the range of 30 to 100 emu / g, and more preferably in the range of 50 to 80 emu / g. The definition of saturation magnetization is described below.

<Core particles>
The carrier comprises core particles. Known magnetic particles can be used as the core particles, but particles containing ferrite components (ferrite particles) are preferred. Ferrite-based particles have high saturation magnetization and can provide carriers with low density. For this reason, carrier adhesion to the photoconductor hardly occurs, and an image with high dot reproducibility can be obtained due to soft spike formation. Known ferrite particles can be used, such as zinc ferrite, nickel ferrite, copper ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, copper-magnesium ferrite, manganese-zinc ferrite, Examples of the particles include manganese-copper-zinc ferrite.

The core particles preferably have a volume resistivity of 1 × 10 ⁶ to 1 × 10 ¹¹ Ω · cm when measured by a bridge method. Ferrite particles having a volume resistivity in this range are generally used because they are inexpensive. When the volume resistivity is low, fog may occur due to poor electrical insulation. On the other hand, when the volume resistivity increases, the counter charge remaining on the surface of the carrier tends to cause an edge effect at the periphery of the solid image and a decrease in image density. The volume resistivity is more preferably in the range of 1 × 10 ^{8 to} 5 × 10 ¹⁰ Ω · cm. The definition of volume resistivity is described below.

Ferrite particles can be produced by a known method. For example, ferrite raw materials such as Fe ₂ O ₃ and Mg (OH) ₂ are mixed, and this mixed powder is heated in a heating furnace and calcined. After cooling the obtained calcined product, it is pulverized by a vibration mill so as to become particles of about 1 μm, and a dispersant and water are added to the pulverized powder to prepare a slurry. This slurry is wet pulverized with a wet ball mill, and the resulting suspension is granulated and dried with a spray dryer to obtain ferrite-based particles.

<Coating layer>
The coating layer is not particularly limited, and any layer made of a known resin can be used. For example, a layer made of acrylic resin or silicone resin can be used.

  Examples of the acrylic resin include polyacrylate, polymethyl methacrylate, polyethyl methacrylate, poly-n-butyl methacrylate, polyglycidyl methacrylate, polyfluorinated acrylate, styrene-methacrylate copolymer, styrene-butyl methacrylate copolymer, and styrene. -Ethyl acrylate copolymer is exemplified. Commercially available product names include: Mitsubishi Rayon Co., Ltd. Dianal SE-5437, SE-5102, SE-5377, SE-5649, SE-5466, SE-5482, HR-169, HR-124, HR-1127, HR -116, HR-113, HR-148, HR-131, HR-470, HR-634, HR-606, HR-607, LR-1065, LR-574, LR-143, LR-396, LR-637 , LR-162, LR-469, LR-216, BR-50, BR-52, BR-60, BR-64, BR-73, BR-75, BR-77, BR-79, BR-80, BR -83, BR-85, BR-87, BR-88, BR-90, BR-93, BR-95, BR-100, BR-101, BR-102, BR-105, R-106, BR-107, BR-108, BR-112, BR-113, BR-115, BR-116, BR-117, Sleksui PSE-0020, SE-0040, SE-0070, SE manufactured by Sekisui Chemical Co., Ltd. -0100, SE-1010, SE-1035, Sanyo Chemical Industries Himer ST95, ST120, Mitsui Chemicals FM601 and the like.

  Examples of the silicone resin include silicone varnish (manufactured by Toshiba Corporation: TSR115, TSR114, TSR102, TSR103, YR3061, TSR110, TSR116, TSR117, TSR108, TSR109, TSR180, TSR181, TSR187, TSR144, TSR165, Shinetsu Chemical Co., Ltd .: KR271) , KR272, KR275, KR280, KR282, KR267, KR269, KR211, KR212), alkyd-modified silicone varnish (manufactured by Toshiba: TSR184, TSR185), epoxy-modified silicone varnish (manufactured by Toshiba: TSR194, YS54), polyester-modified silicone varnish (Toshiba: TSR187), acrylic modified silicone varnish (Toshiba: TSR170, TSR171), U Tan modified silicone varnish (Toshiba Corporation: TSR175), reactive silicone resin (Shin-Etsu Chemical Co., Ltd.: KA1008, KBE1003, KBC1003, KBM303, KBM403, KBM503, KBM602, KBM603, and the like.

  In particular, carriers equipped with a layer of straight silicone resin (alkyl-substituted silicone resin) are less likely to cause toner components (binder resin) to adhere to the surface (filming), and can maintain the toner's ability to impart charge over a long period of time. preferable.

  The straight silicone resin is not particularly limited, and a silicone resin commonly used in this field can be used, but a crosslinkable silicone resin is preferable. As shown below, the crosslinkable silicone resin is a known silicone resin that is cured by crosslinking between hydroxyl groups bonded to Si atoms or a hydroxyl group and a group -OX by a heat dehydration reaction, a room temperature curing reaction, or the like.

  As the crosslinkable silicone resin, either a heat curable silicone resin or a room temperature curable silicone resin can be used. In order to crosslink the thermosetting silicone resin, it is necessary to heat the resin to about 200 to 250 ° C. Although heating is not required to cure the room temperature curable silicone resin, it is preferably heated at 150 to 280 ° C. in order to shorten the curing time. Among the cross-linked silicone resins, those in which the monovalent organic group represented by R is a methyl group are preferable. Since the crosslinked silicone resin in which R is a methyl group has a dense crosslinked structure, when the resin coating layer of the carrier core material is formed using the crosslinked silicone resin, a good carrier such as water repellency and moisture resistance can be obtained. can get. However, if the cross-linked structure becomes too dense, the resin coating layer tends to become brittle, so selection of the molecular weight of the cross-linked silicone resin is important. Moreover, it is preferable that the weight ratio (Si / C) of silicon and carbon in the crosslinkable silicone resin is 0.3 to 2.2. If Si / C is less than 0.3, the hardness of the resin coating layer is lowered, and the carrier life and the like may be lowered. If Si / C exceeds 2.2, the charge imparting property of the carrier to the toner is likely to be affected by temperature change, and the resin coating layer may become brittle. In the present invention, a commercially available cross-linked silicone resin can be used. KR280, KR282, KR261, KR260, KR255, KR266, KR251, KR155, KR152, KR214, KR220, X-4040-171, KR201, KR5202, and KR3093 (all are trade names, manufactured by Shin-Etsu Chemical Co., Ltd.) . The cross-linked silicone resin can be used alone or in combination of two or more.

  A conductive material can be further added to the coating layer. The conductive material is not particularly limited as long as the volume resistivity of the carrier can be controlled. For example, silicon oxide, alumina, carbon black, graphite, zinc oxide, titanium black, iron oxide, titanium oxide, tin oxide, potassium titanate, calcium titanate, aluminum borate, magnesium oxide, barium sulfate, calcium carbonate, etc. Materials.

  Among these conductive materials, carbon black is preferable from the viewpoint of production stability, cost, and low electrical resistance.

  The type of carbon black is not particularly limited, but those having a DBP (dibutyl phthalate) oil absorption in the range of 90 to 170 ml / 100 g are preferred from the viewpoint of excellent production stability. Moreover, since the primary particle diameter is 50 nm or less because of excellent dispersibility, it is particularly preferable. A conductive material can be used individually by 1 type, or can use 2 or more types together.

  The content of the conductive material is expressed in parts by weight with respect to 100 parts by weight of the resin constituting the coating layer. As a content rate of a electrically conductive material, 0.1-20 weight part is preferable with respect to 100 weight part of resin. If it is less than 0.1 part by weight, conductivity may not be obtained. On the other hand, when the amount exceeds 20 parts by weight, there is a possibility that charge leakage occurs due to excessive conductivity. Moreover, it is preferable that it is 3.0-10.0 weight part, and, as for the content rate of the electrically conductive material contained in a 1st coating layer, it is more preferable that it is 3.0-7.0 weight part. Carrier content phenomenon can be improved because a content rate is this range. On the other hand, the content of the conductive material contained in the second coating layer is preferably 7.0 to 25.0 parts by weight, and more preferably 15.0 to 25.0 parts by weight. When the content is within this range, an increase in charge amount can be prevented.

  A charge improving agent can be added to the coating layer. The charge improver is not particularly limited as long as it improves the chargeability of the toner. For example, a nitrogen-containing resin such as a melamine resin can be used for a negatively charged toner, and a fluorine-based resin can be used for a positively charged toner.

The carrier of the present invention having a coating layer may cause carrier adhesion to the photoreceptor when the volume resistivity is low, and the toner charge amount is likely to increase when the volume resistivity is high. Therefore, the volume resistivity is preferably in the range of 1 × 10 ^{8 to} 5 × 10 ¹² Ω · cm, and more preferably in the range of 1 × 10 ^{9 to} 5 × 10 ¹¹ Ω · cm. The definition of volume resistivity is described below.

  A well-known method can be employ | adopted for the formation method of a coating layer. For example, there is an immersion method in which the raw material of the coating layer is dissolved in a solvent (for example, an organic solvent such as toluene or acetone), and the core particles are immersed in the obtained solution. Further, there is a spray method in which a raw material solution for the coating layer is sprayed on the core particles. Furthermore, there is a fluidized bed method in which the raw material solution of the coating layer is sprayed in a state where the core particles are suspended by the fluidized air. Furthermore, there is a kneader coater method in which the core particles and the raw material solution of the coating layer are mixed in a kneader coater to remove the solvent. The conductive material can be added together with the resin to the raw material solution of the coating layer.

<Career>
Carriers used in Examples and Comparative Examples were produced by the following method.

After mixing the ferrite raw material (manufactured by KDK) in a ball mill, calcining at 900 ° C. in a rotary kiln, the obtained calcined powder is average particle size of 2 μm or less by a wet pulverizer (using steel balls as a grinding medium) Until finely ground. The obtained ferrite powder was granulated by a spray drying method, and the granulated product was fired at 1300 ° C. After firing, core particles made of a ferrite component having a volume average particle diameter of 43 μm and a volume resistivity of 1 × 10 ⁹ Ω · cm were obtained by crushing using a crusher.

  Next, 100 parts by weight of dimethyl silicone resin (manufactured by Toshiba Silicon Corporation) and 5 parts by weight of carbon black (manufactured by Mitsubishi Chemical Corporation) are used as coating liquids for forming a thermosetting silicone resin layer covering core particles. Were dissolved in 1000 parts by weight of toluene and adjusted. The core particles were coated with a dipping method coating apparatus in which the core particles were immersed in the prepared coating liquid. Thereafter, the solvent was completely removed by evaporation, and then thermosetting was performed at 230 ° C. for 30 minutes to prepare a carrier C1.

The carrier C1 had a volume average particle size of 40 μm, a volume resistivity of 2 × 10 ¹¹ Ω · cm, and a saturation magnetization of 60 emu / g.

<Toner>
Toners used in Examples and Comparative Examples were prepared by the following method.

The toner material is described below.
Binder resin (polyester resin obtained by polycondensation using bisphenol A propylene oxide, terephthalic acid or trimellitic anhydride as a monomer: glass transition temperature 60 ° C., softening temperature 115 ° C .: manufactured by Fujikura Kasei Kogyo Co., Ltd.) 100 parts by weight Colorant (CI Pigment Blue 15: 3) 5 parts by weight Charge control agent (boron compound: LR-147 manufactured by Nippon Carlit Co., Ltd.) 2 parts by weight Release agent (Microcrystalline wax: Nippon Seiki Co., Ltd.) HNP-9) 3 parts by weight

  The toner material was mixed with a Henschel mixer for 10 minutes, and then melt-kneaded and dispersed with a kneading and dispersing apparatus (Mitsui Mining Co., Ltd .: Needix MOS140-800). The kneaded product was coarsely pulverized with a cutting mill and then finely pulverized with a jet pulverizer (manufactured by Nippon Pneumatic Kogyo Co., Ltd .: IDS-2 type). The finely pulverized product was classified using an air classifier (manufactured by Nippon Pneumatic Industry Co., Ltd .: MP-250 type) to obtain colored resin particles having a volume average particle size of 6.0 μm.

  To 100 parts by weight of the obtained colored resin particles, 1 part by weight of silica particles having a number average particle diameter of 7 nm (manufactured by Degussa) whose surface was hydrophobized with hexamethyldisilazane was added, and the tip speed of the stirring blade was 15 m / The negatively chargeable toner T1 was produced by stirring for 2 minutes with an airflow mixer (manufactured by Mitsui Mining Co., Ltd .: Henschel mixer) set to 2 seconds.

<Two-component developer>
By mixing the carrier C1 and the toner T1, two-component developers used in Examples and Comparative Examples were produced. As the two-component developer, 6 parts by weight of toner and 94 parts by weight of carrier were put into a Nauta mixer (trade name: VL-0, manufactured by Hosokawa Micron Corporation), and mixed and stirred for 20 minutes to prepare a two-component developer G1.

<Image forming apparatus>
An image forming apparatus similar to the image forming apparatus having the configuration shown in FIG. 1 is used as the image forming apparatus used in the example and the comparative example, and only the image forming unit 1 among the four image forming units is formed. Used. As the development conditions of the image forming apparatus, the peripheral speed of the photosensitive member is 400 mm / second, the peripheral speed of the developing roller is 560 mm / second, the gap between the photosensitive member and the developing roller is 0.40 mm, and the gap between the developing roller and the regulating blade is 0. The surface potential of the photosensitive drum (−600 V) and the developing bias (−450 V) were adjusted. A4 size electrophotographic paper (multi receiver: manufactured by Sharp Document System) was used as a test paper.

<Image evaluation method>
Five white image samples were printed and the fog density was measured. For the fog density, the density of the non-image area (0% density) was calculated by the following procedure.

  Using a whiteness meter (Nippon Denshoku Industries Co., Ltd .: Z-Σ90 COLOR MEASURING SYSTEM), the whiteness of the paper before printing is measured in advance. Next, the whiteness in the non-image area of the paper after printing is measured using a whiteness meter, and the difference from the whiteness before printing is obtained. This difference is the fog density. The fog density is less than 0.6 (a state in which fog is hardly visible to the naked eye), 0.6 to less than 1.0 is slightly poor, and 1.0 or more (a state in which fog is clearly visible to the naked eye) is poor. .

Example 1
The two-component developer G1 was set in the image forming apparatus, and after printing 30K text images with 3% coverage, the image forming apparatus was turned off and left for 48 hours. After being allowed to stand, the image forming apparatus was turned on, and gray development was performed for 60 seconds under conditions of a developing bias of +10 V and a photosensitive drum surface potential of 0 V (charging device OFF).

  Thereafter, as described above, five white image samples were printed and the fog density was measured. As a result, the fog density of the five white image samples was in the range of 0.3 to less than 0.6, and the fog was visually observed with the naked eye. Good results were obtained with almost no visible.

(Comparative Example 1)
The two-component developer G1 was set in the image forming apparatus, and after printing 30K text images with 3% coverage, the image forming apparatus was turned off and left for 48 hours. After being left, immediately after the image forming apparatus was turned on, five white image samples were printed without performing gray development. As a result of measuring the fog density, the fog density of the five image samples was 0.7 to 1.1, and the result that the fog was visible even with the naked eye was somewhat poor.

1 is a schematic diagram illustrating an entire image forming apparatus 100 according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a main part of the image forming apparatus 1. It is a timing chart which shows the operation timing and application timing of a drum motor, a control grid voltage, and a development bias. 6 is a graph showing the rise of the surface potential of the photosensitive drum 16; It is a timing chart which shows the operation timing and application timing of a drum motor, a control grid voltage, and a development bias at the time of gray development.

Explanation of symbols

1, 2, 3, 4 Image forming unit 16 Photosensitive drum 17 Charging device 18 Exposure device 19 Developing device 20 Cleaning device 25 Static elimination lamp 26 Fog density sensor 100 Image forming device

Claims (7)

Two-component development comprising a photosensitive drum, a charging device for charging the surface of the photosensitive drum to a specified potential, an exposure device for forming an electrostatic latent image on the photosensitive drum charged by the charging device, and a toner and a carrier In an image forming apparatus comprising: a developing device that contains an agent and develops the electrostatic latent image; and a developing bias supply unit that applies a developing bias to the developing device.
After the power is turned on and before starting the developing operation by the developing device, a pre-processing operation for operating the photosensitive drum and the developing device for a predetermined time while applying a developing bias value lower than the developing bias value applied in the developing operation is performed. An image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the preprocessing operation is performed so that a toner density ID on the surface of the photosensitive drum is 0.5 or less.   3. The image forming apparatus according to claim 1, wherein, in the preprocessing operation, a developing bias potential is applied for 5 seconds to 60 seconds.   The image forming apparatus according to claim 1, wherein in the preprocessing operation, a potential difference between a surface potential of the photosensitive drum and a developing bias potential is less than ± 100V.   The image forming apparatus according to claim 1, wherein the toner includes an external additive having a number average particle diameter of 80 nm to 300 nm.   The image forming apparatus according to claim 1, wherein the carrier is a coating carrier coated with a thermosetting silicone resin.   The image forming apparatus according to claim 1, wherein the core particle includes a ferrite component.

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