JP4194954B2 - Development device - Google Patents

Description

  The present invention relates to a developing device, and more particularly to a developing device using a one-component developer.

  As developing devices for visualizing an electrostatic latent image formed on an electrostatic latent image carrier with a developer, a one-component developing device using a one-component developer and a two-component developing device using a two-component developer are known. It has been. Recently, one-component developing devices have been widely used from the viewpoints of size reduction, weight reduction, cost reduction, and the like. A general conventional one-component developing device includes a developer carrying member arranged close to or in contact with the electrostatic latent image carrying member, a developer supplying member for supplying the developer to the developer carrying member, and a developer. A layer regulating blade that abuts against the carrier and thins the developer on the developer carrier and applies a charge to the developer by frictional charging is provided.

  In order to perform appropriate development with a one-component developing apparatus, it is very important to form a thin layer of a developer on which a charged charge and a layer thickness are always stable on a developer carrier. The charged charge and layer thickness of the developer layer formed on the developer carrier are determined by the contact state between the layer regulation blade and the developer carrier, and the contact pressure between the layer regulation blade and the developer carrier is If the height is increased, a uniform thin layer of the developer can be formed.

  However, when the contact pressure between the layer regulation blade and the developer carrying member is increased, excessive pressure is applied to the developer at the contact portion. As a result, the developer is fused to the layer regulation blade, thereby developing the developer. White streaks are formed in the layer. Further, the charge amount of the developer becomes insufficient, thereby causing fogging, scattering of the developer, and the like, and the formed image is deteriorated. This problem has become particularly serious in recent years when developers having a low softening point are generally used as the fixing temperature for colorization and energy saving is reduced.

  In recent years, the particle size of the developer has been reduced in order to improve the image quality. Since it is difficult to reduce the particle size of the developer by the pulverization method, the small particle size developer is often produced by a wet method such as a polymerization method.

  According to the wet method, it is easy to produce a developer having a small particle size and a narrow particle size distribution, which is advantageous for improving the image quality. On the other hand, a generally spherical developer is generally obtained, so that the developer slipperiness and There is a demerit that the releasability is very high and the developer can easily pass through the layer regulating blade. In particular, when the particle size of the developer is reduced to 10 μm or less, the layer regulating blade cannot sufficiently regulate the developer, and the amount of developer that can be left uncharged increases. Uncharged developer not only prevents the formation of a uniform developer layer on the developer carrier, but also scatters from the developer carrier without being able to adhere to the developer carrier with a mirror image force. This may cause fogging and image defects in the output image.

  Therefore, increasing the contact pressure of the layer regulating blade against the developer carrying member to improve the regulating force on the developer is effective for preventing excessive slipping of the developer. However, since the stress on the developer is increased, the developer is easily crushed and melted in the layer regulating blade. For this reason, the developer is fused to the layer regulating blade, and coating streaks or the like are generated on the developer carrying member, so that the life of the developing device is remarkably shortened.

  In response to the above-described problems, a developer charging layer is provided separately from the developing blade, and a toner charging member to which an AC voltage is applied in a non-contact manner to the developing roller is provided, thereby reducing a developer thin layer while reducing the stress on the developer. A technique has been proposed in which a sufficient amount of developer charge can be obtained while forming the film (for example, see Patent Document 1).

In addition, a toner charging roller is provided upstream of the developing portion where the developing roller contacts the photosensitive member, and voltage applying means for applying a DC voltage equal to or higher than the discharge start voltage and the same polarity as the developer to the developer is provided. By controlling the voltage application unit based on the detection result of the current detection unit, it is possible to stably apply a charge to the developer by the developing roller for a long period of time and to stabilize the charge amount of the developer. A technique has been proposed (see, for example, Patent Document 2).
JP 2001-75357 A JP 2003-57948 A

  However, also in the techniques of Patent Documents 1 and 2, it is necessary to provide a layer regulating blade (developing blade, elastic blade) that is pressed against the developer carrying member in order to make the developer on the developer carrying member thin. There is a great stress on the developer. For this reason, the developer is fused to the layer regulating blade, white streaks are formed in the developer layer, the charge amount of the developer is insufficient, fogging, scattering of the developer, and the like occur, and the formed image Will deteriorate.

  An object of the present invention is to provide a developing device capable of forming a high-quality developer image by forming a uniformly thinned and charged developer layer on a developer carrier without providing a layer regulating blade. It is to provide.

  The developing device of the present invention is configured as follows in order to solve the above-described problems.

(1) A developer carrying member that carries a developer during a developing operation and transports the developer to a developing region that is opposite to the electrostatic latent image carrying member, and an AC voltage is applied during the developing operation to develop from the developing region. A charging roller disposed upstream of the developer carrying body with a predetermined gap of 40 μm or more and 250 μm or less to charge the developer positioned between the developer carrying body and a developing operation. At the start of the rotation, the application of the AC voltage to the charging roller is started after the rotation of the charging roller is started, and the rotation of the developer carrier is started after the application of the AC voltage to the charging roller is started. Features.

  In this configuration, since the developer carrying member and the charging roller are arranged in a non-contact manner with an appropriate gap, the developer passing between the developer carrying member and the charging roller is subjected to excessive stress. Without being formed on the developer carrying member in a layer having an appropriate uniform thickness. Therefore, there is no need to provide a separate layer regulating blade.

Further, since an AC voltage is applied to the charging roller, a partial charge amount fluctuation is suppressed, and a uniform charged charge is imparted to the developer. Therefore, the developer thinned to an appropriate uniform thickness on the developer carrier is uniformly charged by the charging roller to which an AC voltage is applied.
Furthermore, since the charging roller starts rotating before the AC voltage is applied to the charging roller, the developer is uniformly charged. In addition, since the start timing of rotation of the charging roller and the start timing of rotation of the developer carrier are shifted, the occurrence of clogging of the developer at the position where the charging roller and the developer carrier are opposed to each other is suppressed. Further, since the rotation of the charging roller and the application of the AC voltage to the charging roller are started earlier than the rotation of the developer carrier, the developer that is not sufficiently charged may be conveyed to the development area. This prevents the charging failure of the developer.

  (2) The charging roller is rotatable.

  In this configuration, the charging roller is formed to be rotatable. Since the charging roller is rotatable, the stress on the developer passing between the charging roller and the developer carrier is further reduced. Further, the discharge surface is updated by the rotation of the charging roller.

  (3) A cleaning member for removing the developer attached to the charging roller is further provided on the downstream side in the rotation direction of the charging roller with respect to the position of the charging roller facing the developer carrier.

  In this configuration, since the cleaning member is provided on the charging roller, the developer attached to the charging roller at a position facing the developer carrying member is removed by the cleaning member. As a result, the discharge surface of the charging roller is constantly updated.

  (5) The developer includes at least a binder resin and a colorant, and the concentration of the colorant in the developer is 4% by weight or more and 20% by weight or less.

  In this configuration, a high pigment developer having a colorant concentration of 4% by weight to 20% by weight is used. In this case, a high-quality developer image with a low adhesion amount is formed. Further, the consumption of developer is reduced.

  According to the present invention, the following effects can be obtained.

(1) Since the developer carrying member and the charging roller are arranged in a non-contact manner with an appropriate gap, a developer layer having an appropriate uniform thickness can be formed on the developer carrying member. Therefore, there is no need to provide a separate layer regulating blade. Further, since an AC voltage is applied to the charging roller, the developer can be uniformly charged without unevenness. Therefore, a high-quality developer image can be formed. Further, toner leakage can be prevented.
Also, at the start of the developing operation, the application of AC voltage to the charging roller is started after the rotation of the charging roller is started, and the rotation of the developer carrier is started after the application of the AC voltage to the charging roller is started. Therefore, the occurrence of clogging of the developer at the position where the charging roller and the developer carrying member are opposed to each other can be suppressed, and the charging failure of the developer can be prevented.

  (2) By rotating the charging roller, the discharge surface can be updated and the life of the charging roller can be extended.

  (3) Since the developer attached to the charging roller is removed by the cleaning member, the discharge surface of the charging roller can be constantly updated, and the life of the charging roller can be extended.

( 4 ) Since a high pigment developer is used, a high-quality developer image can be formed with a low adhesion amount, and the consumption of the developer can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a developing device 10 according to an embodiment of the present invention. The developing device 10 according to this embodiment includes a developing roller 1, a toner supply roller 2, a cleaning member 3 for the toner supply roller 2, a charging roller 5, a cleaning member 6 for the charging roller 5, and a current monitor 4. The developing roller 1, the toner supply roller 2, the cleaning member 3, the charging roller 5, and the cleaning member 6 are accommodated together with the toner 8 in a developing tank (not shown). In this embodiment, a one-component developer (toner) having a predetermined particle diameter of 4 μm or more and 8 μm or less is used.

  The developing roller 1 is disposed in opposition to the photosensitive drum 7 that is an electrostatic latent image carrier and is driven to rotate counterclockwise in FIG. The developing roller 1 is configured such that the surface of a metal material such as aluminum is coated with a porous elastic body such as a sponge. As the elastic body, a rubber material such as urethane, silicone, EPDM (ethylene propylene), and the rubber material added with a conductive agent such as carbon black and ions are used. Irregularities of several tens of μm are formed. A developing bias voltage is supplied to the developing roller 1 from a developing bias power supply circuit, and the developing bias voltage causes the toner 8 to adhere to the electrostatic latent image formed on the photosensitive drum 7, and other regions, that is, non-images. The polarity and voltage value are set so that the toner 8 does not adhere to the region.

  The toner supply roller 2 is disposed so that a part of the peripheral surface thereof is in contact with the developing roller 1, and is driven to rotate in the same direction as the developing roller 1, that is, counterclockwise in FIG. The toner supply roller 2 is configured using the same material as the developing roller 1. Note that a larger amount of foaming agent than that of the developing roller 1 may be used as the material of the toner supplying roller 2 in order to make the elasticity of the toner supplying roller 2 greater than that of the developing roller 1. A bias voltage in the direction of moving the toner 8 toward the developing roller 1 is applied to the toner supply roller 2 from the bias power supply circuit.

  For example, the peripheral speed Vp of the photosensitive drum 7 is set to Vp = 130 (mm / sec), whereas the peripheral speed Vd of the developing roller 1 is set to Vd = 117 (mm / sec). The peripheral speed ratio is Vd / Vp = 0.9. The peripheral speed Vs of the toner supply roller 2 is set to Vs = 234 (mm / sec), and the peripheral speed ratio with the developing roller 1 is Vd / Vs = 0.5. The contact depth of the toner supply roller 2 with respect to the developing roller 1 is set to 0.5 mm, for example.

  The peripheral speed Vp of the photosensitive drum 7 is within a range of Vp = 25 to 300 (mm / sec), and the peripheral speed Vd of the developing roller 1 is within a range of Vd = 25 to 450 (mm / sec). May be set so that Vd / Vp = 1-2. The peripheral speed Vs of the toner supply roller 2 is set so that the peripheral speed ratio with the developing roller 1 is Vs / Vd = 0.5 to 2 within a range of Vs = 25 to 450 (mm / sec). That's fine. Further, the contact depth of the toner supply roller 2 with respect to the developing roller 1 is set to 0.2 mm to 2 mm.

  The cleaning member 3 for the toner supply roller 2 is disposed in the vicinity of the peripheral surface of the toner supply roller 2 and regulates the amount of toner 8 conveyed by the toner supply roller 2.

  The charging roller 5 is upstream of the developing area where the developing roller 1 and the photosensitive drum 7 are opposed to each other in the rotation direction of the developing roller 1 and downstream of the contact position between the developing roller 1 and the toner supply roller 2. On the side, a predetermined gap of 40 μm or more and 250 μm or less is provided with the developing roller 1.

  The charging roller 5 is made of a metal material, a hard resin material, or the like, and is driven to rotate in the same direction as the developing roller 1, that is, counterclockwise in FIG. An AC voltage is superimposed on the DC voltage and applied to the charging roller 5. A predetermined gap is provided between the developing roller 1 and the charging roller 5, the charging roller 5 has a roller shape, and the charging roller 5 rotates, so that it passes between the charging roller 5 and the developing roller 1. The stress on the toner 8 is reduced. In addition, rotation of the charging roller 5 updates the discharge surface of the charging roller 5, thereby extending the life of the charging roller.

  The DC voltage is controlled such that the current value detected by the current monitor 4 becomes a predetermined constant value. Since the direct current component contributing to the charge amount of the toner 8 is controlled to be a constant value, the influence of the discharge distance, the atmospheric pressure, the resistance fluctuation of the charging roller 5 and the like can be minimized, and the change of the discharge impedance is small. Thus, the toner 8 can always be charged to a stable charge level.

  As shown in FIG. 2, the AC voltage has a crest value on the same polarity side (minus) as the charging polarity of the toner 8 larger than the discharge start voltage, and a wave on the charging polarity and reverse polarity side (plus) of the toner 8. The high value is controlled to be smaller than the discharge start voltage.

  The toner 8 accommodated in the developing device 10 is conveyed by the toner supply roller 2 and is charged by friction between the development roller 1 and the toner supply roller 2 at a contact position between the development roller 1 and the toner supply roller 2. Then, the toner is conveyed to a charging region between the developing roller 1 and the charging roller 5. The toner 8 conveyed to the charging region is regulated in its conveyance amount by the charging roller 5 to be a uniform thin layer on the developing roller 1, and the developing roller 1 and the charging roller 5 are discharged by air discharge from the charging roller 5. Is further charged to a predetermined polarity while reciprocating between the two. In this reciprocating motion, the polarity of the toner 8 charged to the opposite polarity by the electric field discharged in the air from the charging roller 5 is corrected, and the charged surface of the toner 8 is updated by vibration, The toner 8 is uniformly charged.

  Thus, by setting the distance between the developing roller 1 and the charging roller 5 to a predetermined distance of 40 μm or more and 250 μm or less, and charging the toner 8 while reciprocating between the developing roller 1 and the charging roller 5, Even when a plurality of layers of toner 8 are formed on the developing roller 1, generation of uncharged toner, weakly charged toner, and reversely charged toner can be prevented, and all the toners 8 can be uniformly charged uniformly. As a result, it is possible to prevent occurrence of fogging and density reduction in the formed image and form a high-quality image.

  Here, assuming that the charge amount q / m (C / kg) of the toner 8 is substantially constant regardless of the particle diameter of the toner 8, the acceleration α acting on the toner 8 is expressed by the following equation (1). .

  Therefore, the relational expression [Equation 2] holds.

  Further, the relational expression [Formula 3] is established from the relational expression [Formula 2].

  FIG. 3A is a diagram showing the relationship between the distance gap between the developing roller 1 and the charging roller 5 and the electric field strength Em between them, and FIG. 3B is a diagram showing the development when the discharge start voltage Vth is applied. It is a figure which shows the relationship between distance gap of the roller 1 and the charging roller 5, and the electric field strength Em between both in a matrix form.

When the distance gap between the developing roller 1 and the charging roller 5 is larger than 250 μm, the electric field intensity Em necessary for reciprocating the toner 8 cannot be obtained, whereas when the distance gap is smaller than 250 μm. The electric field intensity Em begins to increase rapidly in spite of the decrease of the discharge start voltage Vth to 1862 (V) or less, and the toner 8 can be efficiently reciprocated and charged. The electric field intensity Em is 14 when the distance gap is 40 μm.
(MV / m), and the toner 8 can be charged by reciprocating particularly efficiently.

  Further, the thickness of the OPC photoreceptor is about 20 μm, and the withstand voltage of the photoreceptor layer is about 2 kV. As can be seen from FIG. 3B, by setting the distance gap to 250 μm or less, the discharge start voltage Vth can be suppressed to 2 kV or less, which is the withstand voltage of the photoreceptor layer. Therefore, even when a foreign matter such as paper dust is clogged between the photosensitive drum 7 and the charging roller 5 and the applied voltage of the charging roller 5 is directly applied to the photosensitive drum 7, the photosensitive layer of the photosensitive drum 7. Does not break down.

  Further, since the toner layer thickness on the developing roller 1 is 10 μm to 20 μm and the arrangement accuracy of the charging roller 5 is about 10 μm to 20 μm, the distance gap between the developing roller 1 and the charging roller 5 is set to 40 μm or more. This prevents the charging roller 5 from coming into direct contact with the toner layer on the developing roller 1 to cause abnormal charging or toner aggregation. On the other hand, when the distance gap is smaller than 40 μm, the reciprocating motion of the toner 8 becomes insufficient and is not sufficiently charged, and uncharged toner or weakly charged toner may be generated, which is not preferable.

  The frequency of the AC voltage applied to the charging roller 5 is preferably 500 Hz or more and 5 KHz or less. When the frequency exceeds 5 KHz, the reciprocating motion of the toner 8 may not be able to follow, which is not preferable.

  The cleaning member 6 for the charging roller 5 is disposed downstream of the charging region in the rotation direction of the charging roller 5 so as to contact the peripheral surface of the charging roller 5, and the toner 8 attached to the charging roller 5 in the charging region. Scrap off. Since the toner 8 attached to the charging roller 5 is removed by the cleaning member 6, the discharge surface of the charging roller 5 is constantly updated, the life of the charging roller 5 is extended, and the charging capability of the charging roller 5 is maintained for a long period. .

  At the start of the developing operation of the developing device 10, the rotation driving of the charging roller 5 is started and then the application of the DC voltage and the AC voltage to the charging roller 5 is started, and the application of the DC voltage and the AC voltage to the charging roller 5 is started. After the start, the rotational driving of the developing roller 1 is started. Since the charging roller 5 starts to rotate before the DC voltage and the AC voltage are applied to the charging roller 5, the toner 8 is uniformly charged. In addition, since the start timing of rotation of the charging roller 5 and the start timing of rotation of the developing roller 1 are shifted, occurrence of clogging of the toner 8 at the position (charging region) where the charging roller 5 and the developing roller 1 are opposed is suppressed. Is done. Further, since the rotation of the charging roller 5 and the application of the DC voltage and the AC voltage to the charging roller 5 are started earlier than the rotation of the developing roller 1, the toner 8 which is not sufficiently charged is conveyed to the developing region. This prevents the toner 8 from being poorly charged.

  According to the developing device 10, the developing roller 1 and the charging roller 5 are arranged in a non-contact manner with an appropriate gap, so that a layer of the toner 8 having an appropriate uniform thickness is formed on the developing roller 1. Can do. Therefore, there is no need to provide a separate layer regulating blade. Further, since an AC voltage is applied to the charging roller 5, the toner 8 can be uniformly charged without unevenness. Therefore, a high-quality developer image can be formed. In addition, since the toner can be charged uniformly, toner leakage due to toner scattering can be prevented.

  The toner used in this embodiment includes, for example, at least a binder resin and a colorant, the toner has a softening point of 95 ° C. or more and 120 ° C. or less, and a volume average particle diameter of 4 μm or more and 8 μm or less. Toner 8 having a colorant concentration in the toner of 4 wt% or more and 20 wt% or less and an average circularity of 0.95 or more and 1.0 or less is used.

  The average circularity of the toner 8 is a numerical value measured by a flow type particle image analyzer FPIA-2000 (manufactured by Sysmex Corporation). Specifically, about 1000 to 10000 toner particles are projected as a projected image, their projected area A, its peripheral length L, and the area AL of a perfect circle having the peripheral length L are calculated. The average circularity of the toner is used. The toner 8 as described above is preferable for lowering the fixing temperature (energy saving) and improving the image quality. On the other hand, the conventional developing device tends to cause fusion, and the charge tends to be non-uniform. Can be used sufficiently and can form a high-quality image.

  The binder resin used in the toner used in the present invention is not particularly limited as long as it is a toner resin used in general electrophotographic technology. Specifically, as a binder resin used for the toner, styrene such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene, and a homopolymer of a substituted product thereof, styrene-p-chlorostyrene copolymer, styrene-propylene Copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-meta Methyl acrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethacrylate methyl copolymer, styrene-acrylonitrile copolymer, styrene-vinyl Methyl ether copolymer, styrene-vinyl methyl ketone Styrene copolymers such as polymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-acrylonitrile-indene copolymers, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, silicone resins, polyester resins , Polyurethane resin, polyamide resin, epoxy resin, polyvinyl butyral, rosin modified resin, terpene resin, phenol resin, xylene resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, etc. , Used alone or in combination of two or more. In particular, a polyester resin having a softening point of 95 ° C. or higher and 120 ° C. or lower is preferable as a binder resin for a full color toner from the viewpoint of thermal characteristic control.

  The colorant used in the toner used in the present invention is not particularly limited as long as it is a toner colorant used in general electrophotographic technology. For example, as colorants used in toners, in addition to carbon black and nigrosine dyes conventionally used for monochrome, dyes such as azo dyes, anthraquinone dyes, indigo dyes, phthalocyanine dyes, xanthene dyes Azo pigments, benzimidazolone pigments, quinacridone pigments, phthalocyanine pigments, isoindolinone pigments, isoindoline pigments, dioxazine pigments, anthraquinone pigments, perylene pigments, perinone pigments, thioindigo pigments, Organic pigments such as quinophthalone pigments and metal complex pigments, inorganic pigments such as titanium oxide, carbon black, molybdenum red, chrome yellow, titanium yellow, chromium oxide, and Berlin blue, and metal powders such as aluminum powder Such as well-known It can be used as a dye or pigment.

  In the toner used in the present invention, a release agent, a charge control agent, a fluidity improver, a fixing accelerator, and a conductive agent are selectively added as necessary.

  The toner 8 having a volume average particle diameter of 4 μm or more and 8 μm or less used in this embodiment is manufactured not by a conventional kneading pulverization method but by a wet method represented by an emulsion polymerization method, a suspension polymerization method, and a solution suspension method. It is preferred that According to this, there is an advantage that the small particle size and particle size distribution of the toner can be easily controlled, and the toner structure can be controlled by controlling the polarity and process of the material.

  FIG. 4 is a diagram showing experimental results in two examples and four comparative examples.

  (Example 1) As a toner, 100 parts by weight of polyester, 5.4 parts by weight of quinacridone pigment, 3 parts by weight of a low melting point wax are added and manufactured by a wet method, the softening point is 108 ° C, and the volume average particle diameter is A toner having 4 μm and a negative charge polarity was used. The developing device 10 shown in FIG. 1 was used as the developing device, and the distance gap between the developing roller 1 and the charging roller 5 was set to 40 μm.

In the actual image test, the developing device AR-C260M manufactured by Sharp Corporation was modified to the same structure as the developing device 10 shown in FIG. Prepared to 0.6 mg / cm ² and printed a solid image of 40 mm square in a normal temperature and humidity environment, the image density of the solid image, the whiteness (fogging) of the non-image area after printing, and fixing Sex was evaluated.

  (Embodiment 2) A live-action test was performed in the same manner as in Embodiment 1 except that the same developing device as in Embodiment 1 was used, the toner particle diameter was set to 8 μm, and the distance gap between the developing roller 1 and the charging roller 5 was set to 250 μm. Carried out.

  (Comparative Example 1) Using the same toner and developing device as in Example 1, the actual shooting test was performed in the same manner as in Example 1 except that the distance gap between the developing roller 1 and the charging roller 5 was set to 20 μm.

  (Comparative Example 2) Using the same toner and developing device as in Example 1, and using the same shooting test as in Example 1, except that the distance gap between the developing roller 1 and the charging roller 5 was set to 400 µm.

  (Comparative Example 3) Using the same developing apparatus as in Example 1, a live-action test was conducted in the same manner as in Example 1 except that the amount of quinacridone pigment added was changed to 2.1 parts by weight.

  (Comparative Example 4) Using the same developing device as in Example 1, a live-action test was conducted in the same manner as in Example 1 except that the amount of quinacridone pigment added was changed to 34.3 parts by weight.

  The solid images obtained in the above-described examples and comparative examples were evaluated by the following methods.

  The image density was measured with an X-Rite 938 spectrocolorimetric densitometer (manufactured by Nihon Hakusho Kaisha Co., Ltd.), and judged to be good if the image density was 1.2 or higher.

  The whiteness is measured using a SZ90 type spectroscopic color difference meter manufactured by Nippon Denka Kogyo Co., Ltd. Color differences X, Y, and Z were acquired, and it was determined that the value was good if the value of Z was 0.5 or less.

  Fixability is determined by measuring the change in image density before and after rubbing with a reflection densitometer in a rubbing test in which an eraser applied with a 1 kg load is reciprocated three times on a fixed image of a predetermined density, and measuring the residual ratio of the image. To evaluate. Specifically, the above-mentioned rubbing test was performed on seven points having different concentrations, a graph was created, and the minimum residual ratio among the seven points was evaluated. If the minimum residual rate was 60% or more, it was determined to be a pass (◯).

  In the comprehensive evaluation, the results of the image density, whiteness and fixability tests are comprehensively judged. If all the tests give good results, ○ In the case of △, two or more tests were evaluated to be defective, and in the case of obtaining a result of ×, the evaluation was made in three stages.

  In Examples 1 and 2, the distance gap between the developing roller 1 and the charging roller 5 was set within an appropriate range, and good results were obtained in all tests of image density, whiteness, and fixability.

  In Comparative Example 1, reduction in image density and occurrence of fogging were observed. This is because the distance gap between the developing roller 1 and the charging roller 5 is set to be smaller than the appropriate range, and the toner cannot reciprocate between the developing roller 1 and the charging roller 5. This is probably because the toner could not be uniformly charged and a large amount of uncharged or weakly charged toner was generated.

  In Comparative Example 2, reduction in image density and occurrence of fogging were observed. This is because the distance gap between the developing roller 1 and the charging roller 5 is set to be larger than the appropriate range, and the electric field strength necessary for reciprocating the toner cannot be obtained. This is probably because the toner could not be uniformly charged and a large amount of uncharged or weakly charged toner was generated.

  In Comparative Example 3, a decrease in image density was observed. This is because the concentration of the colorant in the toner is set lower than 4% by weight, so that the transparency is good, but the concealing property is insufficient, and a uniform high-density image cannot be obtained. This is probably because

  In Comparative Example 4, a sufficient fixing property of the image could not be obtained. This is probably because the colorant concentration in the toner is set higher than 20% by weight, so that the ratio of the resin component is reduced and sufficient fixing strength cannot be obtained.

  From Examples 1 and 2 and Comparative Examples 1 to 4, when the distance gap between the developing roller 1 and the charging roller 5 is set to 40 μm or more and 250 μm or less in the developing device 10 shown in FIG. It was confirmed that a good image can be formed by charging. Further, it was confirmed that when the concentration of the colorant in the toner used in the developing device 10 is set to 4% by weight or more and 20% by weight or less, a good image can be formed.

1 is a diagram illustrating a schematic configuration of a developing device according to an embodiment of the present invention. It is a wave form diagram of the alternating voltage applied to a charging roller. (A) is a figure which shows the relationship between the distance gap of a developing roller and a charging roller, and the electric field strength Em between both, (b) is a developing roller and charging roller when the discharge start voltage Vth is applied. It is a figure which shows the relationship between the distance gap of and the electric field strength Em between both in a matrix form. It is a figure which shows the experimental result in two Examples and four comparative examples.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing roller 4 Current monitor 5 Charging roller 6 Cleaning member 7 Photosensitive drum 8 Toner 10 Developing device

Claims (4)

A developer carrying member that carries the developer during the developing operation and conveys the developer to a developing region that is opposite to the electrostatic latent image carrying member;
An AC voltage is applied during the developing operation, and a predetermined gap of 40 μm or more and 250 μm or less is provided with respect to the developer carrying member upstream of the developing region in the developer transport direction. A charging roller for charging the developer positioned at
At the start of the developing operation, the application of the AC voltage to the charging roller is started after the rotation of the charging roller is started, and the application of the AC voltage to the charging roller is started after the application of the AC voltage to the charging roller is started. A developing device characterized in that rotation is started .   The developing device according to claim 1, wherein the charging roller is rotatable.   3. The cleaning device according to claim 2, further comprising a cleaning member that removes the developer attached to the charging roller at a downstream side in the rotation direction of the charging roller with respect to a position of the charging roller facing the developer carrier. The developing device described. The developer includes at least a binder resin and a colorant,
The concentration of the colorant in the developer, a developing device according to claim 1, characterized in that 4 to 20% by weight in any of the three.

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