JP2009058895A - Development device, process cartridge, and image-forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image of high quality by using a developer which is high in circularity and small in particle size, and also obtain an excellent image, which is high in quality, for a long period of time. <P>SOLUTION: A development device is provided with; a toner T1 which is accommodated in a development container F and whose volume average particle size is 4.0 μm or more and 6.2 μm or less and average circularity is 0.965 or more; and a toner T2 which is previously applied to the surfaces of a development roller 3 and feeding roller 5 in a state in which the development device D is not used. In this case, a relation between R1 and R2 satisfies an equation 1.0<R2/R1≤1.5, and a relation between H1 and H2 satisfies an equation 1.0<H2/H1≤2.0, wherein R1 represents a volume average particle size of the toner T1, R2 represents a volume average particle size of the toner T2, H1 represents a half value width of a volume particle size distribution of the toner T1, and H2 represents a half value width of a volume particle size distribution of the toner T2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material using an electrophotographic method, and more particularly to a developing device and a process cartridge that are applied to the image forming apparatus.

  As a conventional developing method using one-component toner, a contact developing method using a developing roller having an elastic layer has been proposed.

  FIG. 9 is a schematic diagram showing a conventional developing device, for explaining a contact developing method using a developing roller having an elastic layer.

  There is widely known a method of carrying out development by carrying a non-magnetic developer on a developing roller 103 which is an elastic roller having a dielectric layer and bringing it into contact with the surface of the photosensitive drum 101. The developer is supplied to the developing roller 103 by the supply roller 105 that is in contact with the developing roller 103. The supply roller 105 transports the developer from the developing container, adheres it to the developing roller 103, and also has a function of temporarily removing the developer remaining on the developing roller 103.

  The charge of the developer adhering to the developing roller 103 by layer regulation and frictional charging is performed by bringing the toner regulating member 104 into contact with the developing roller 103. As the toner regulating member 104, it has been proposed to use a blade-shaped member that supports a thin metal plate in a cantilevered manner and abuts the abdominal surface of the opposed portion against the developing roller 103. The developer coated on the developing roller 103 by the toner regulating member 104 converts the electrostatic latent image on the electrostatic latent image formed on the photosensitive drum 101 and the bias potential applied to the developing roller 103. develop.

  In this developing method, the toner regulating member is in contact with the developing roller. Therefore, it has been proposed to apply a coating agent such as a lubricant to the surface of the developing roller in advance before being incorporated in the developing device, thereby preventing the developing roller surface from being damaged due to friction between the layer regulating member and the developing roller. (See Patent Document 1).

In recent years, it has been proposed to reduce the particle size of toner in order to improve image quality (see Patent Document 2).
JP 2002-278262 A JP 2005-215057 A

  However, in the conventional contact development method as described above, when a toner having a high circularity and a small particle diameter is used, the toner layer formation on the developing roller becomes unstable with respect to the environment and the number of prints, There is a concern that an image defect associated therewith may occur. In particular, when an unused developing device is used in a low-temperature and low-humidity environment or after standing for a long period of time, there is a concern that the toner layer formation becomes unstable and a solid white image defect occurs. The solid white image defect is an image defect that causes a density difference of about 1 to 5 mm in the solid white portion due to toner firmly adhered on the surface of the developing roller.

  The present invention has been made in view of the circumstances as described above, and obtains a high-quality image by using a developer having a high degree of circularity and a small particle size. The purpose is to obtain an image.

In order to achieve the above object, the present invention provides:
A developer carrying member carrying the developer;
A developer container containing a developer;
Developer supply means for supplying the developer contained in the developer container to the developer carrier;
A developer amount regulating means for regulating the developer carried on the developer carrying body;
With
In the developing device in which the developer carrying member is provided so as to come into contact with the developing member, and the developing member is developed with the developer,
A first developer housed in the developer container, having a volume average particle size of 4.0 μm or more and 6.2 μm or less, and an average circularity of 0.965 or more;
A second developer pre-applied to the surface of the developer carrier and the surface of the developer supply means in a state where the developing device is not used;
With
When the volume average particle size of the first developer is R1, and the volume average particle size of the second developer is R2, the relationship between R1 and R2 is
1.0 <R2 / R1 ≦ 1.5
The filling,
When the half-value width of the volume particle size distribution of the first developer is H1, and the half-value width of the volume particle size distribution of the second developer is H2, the relationship between H1 and H2 is
1.0 <H2 / H1 ≦ 2.0
It is characterized by satisfying.

  According to the present invention, a high-quality image can be obtained by using a developer having a high degree of circularity and a small particle diameter, and a high-quality and good image can be obtained over a long period of time.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

[Body configuration]
FIG. 2 is a schematic sectional view of an image forming apparatus using the developing device according to the embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of the process cartridge according to the present embodiment.

  An image forming apparatus A shown in FIG. 2 is a full-color laser printer using an electrophotographic process. The overall schematic configuration of the image forming apparatus A in the present embodiment will be described below.

  As shown in FIG. 3, the image forming apparatus A includes a process cartridge B in which a charging device E, a developing device D, a cleaning device C, and a photosensitive drum 1 as an image carrier are integrated, as yellow, magenta, cyan, Each black color is arranged in quadruplicate. A toner (developer) image formed by the process cartridge B of each color is transferred onto an intermediate transfer belt 20 as a transfer unit to form a full color image. The image forming process on the process cartridge B will be described later in detail. Here, the process cartridge B is detachably attached to the image forming apparatus main body. In the process cartridge B, it is sufficient that at least the developing device D and the photosensitive drum 1 are integrated as constituent elements.

  The toner images formed on the photosensitive drums 1 by the process cartridges B for the respective colors are transferred to the primary transfer rollers 22y, 22m, 22c, and 22k provided at positions facing the photosensitive drums 1 for the respective colors with the intermediate transfer belt 20 interposed therebetween. Thus, the image is transferred onto the intermediate transfer belt 20. The toner images transferred onto the intermediate transfer belt 20 are collectively transferred onto the recording material by the secondary transfer roller 23 provided on the downstream side in the moving direction of the intermediate transfer belt 20. The untransferred toner on the intermediate transfer belt 20 is collected by the intermediate transfer belt cleaner 21.

  The recording material P is stacked in a cassette 24 below the image forming apparatus A, and is conveyed by a feeding roller 25 together with a request for a printing operation, and is formed on the intermediate transfer belt 20 at the position of the secondary transfer roller 23. The image is transferred.

  Thereafter, the toner image on the recording material is heated and fixed on the recording material by the fixing unit 26, and is discharged to the outside of the image forming apparatus A through the discharge unit 27.

  In the image forming apparatus A, an upper unit that accommodates detachable process cartridges B of four colors and a lower unit that accommodates a transfer unit, a recording material, and the like are separable. When the jam processing such as a paper jam occurs or when the process cartridge B is replaced, the above processing is performed by opening the upper and lower units.

  Note that in the image forming apparatus A of the present embodiment, the life of the process cartridge B including the toner capacity is set to be equivalent to 20,000 sheets in terms of A4 paper printing rate of 5%.

  Next, an image forming process in the process cartridge B will be described.

  Here, FIG. 3 shows a schematic cross section in the vicinity of one of the four process cartridges B arranged in parallel.

  As the photosensitive drum 1 that is the center of the image forming process, an organic photosensitive drum 1 is used in which an outer peripheral surface of an aluminum cylinder is coated with an undercoat layer that is a functional film, a carrier generation layer, and a carrier transfer layer in this order. In the image forming process, the photosensitive drum 1 is driven by the image forming apparatus A in the direction of arrow a in the figure at a predetermined speed.

  The charging roller 2, which is a charging device, presses and contacts a roller portion of conductive rubber against the photosensitive drum 1, and is driven to rotate in the direction of arrow b. Here, as a charging process, a DC voltage of −1100 V is applied to the core of the charging roller 2 with respect to the photosensitive drum 1, and the surface potential of the photosensitive drum 1 is −550 V due to the electric charge induced thereby. A uniform dark portion potential (Vd) is formed.

  The spot pattern of the laser light emitted by the scanner unit 10 corresponding to the image data on the uniform surface charge distribution surface exposes the photosensitive drum 1 as indicated by an arrow L in FIG. The exposed portion of the photosensitive drum 1 loses its surface charge due to carriers from the carrier generation layer, and the potential decreases. As a result, an electrostatic latent image is formed on the photosensitive drum 1 with the light portion potential Vl = −100 V at the exposed portion and the dark portion potential Vd = −550 V at the unexposed portion.

  The electrostatic latent image is developed by the developing action of the developing device D having a toner coat layer formed on the developing roller 3 having a predetermined coat amount and charge amount.

The method for forming the toner layer will be described later, but the outline will be described here. The developing roller 3 rotates in the forward direction as shown by an arrow c while contacting the photosensitive drum 1. In this embodiment, the toner charged negatively by frictional charging with respect to the DC bias applied to the developing roller 3 of −350 V is in the developing portion where the photosensitive drum 1 comes into contact with the bright portion potential portion. The electrostatic latent image is made into a real image by flying only to the surface.

  The intermediate transfer belt 20 that contacts the photosensitive drum 1 of each process cartridge B is pressed against the photosensitive drum 1 by primary transfer rollers 22 y, 22 m, 22 c, and 22 k that face the photosensitive drum 1. In addition, a DC voltage is applied to the primary transfer rollers 22 y, 22 m, 22 c, and 22 k, and an electric field is formed between the primary transfer rollers 22 y, 22 m, 22 c, and 22 k. As a result, the toner image formed on the photosensitive drum 1 is transferred from the photosensitive drum 1 to the intermediate transfer belt 20 under the force of the electric field in the pressure contact area.

  On the other hand, the untransferred toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 20 is scraped off from the drum surface by the urethane rubber cleaning blade 6 installed in the cleaning device C, and the inside of the cleaning device C It is stored in.

[Examples and Comparative Examples]
First, in order to clarify advantageous effects in the present embodiment, examples and comparative examples applied to the embodiment will be described below.

[Example 1]
FIG. 1 is a schematic cross-sectional view illustrating a developing device D according to the first embodiment. 1A shows the developing device D in use (during operation), and FIG. 1B shows the developing device D in an unused state.

  The developing device D includes a developing container F, a developing roller 3 as a developer carrier, a supply roller 5 as a developer supply unit, and a stirring member 11. Here, the developing container F accommodates a non-magnetic one-component toner T1 (hereinafter, toner T1) as the first developer. The developing roller 3 rotates in the forward direction c while being in contact with the photosensitive drum 1 as a developing object. The supply roller 5 rotates in the reverse direction d while being in contact with the developing roller 3. The agitating member 11 agitates the toner T1.

  Further, a toner regulating member as a developer amount regulating means for abutting the developing roller 3 on the downstream side of the supply roller 5 with respect to the rotation direction c of the developing roller 3 and facing development and regulating the amount of developer. 4 is provided. The toner regulating member 4 is intended to control the toner on the developing roller 3 to a predetermined coating amount and a predetermined charge amount suitable for development on the photosensitive drum 1.

  Here, the volume average particle size R1 is a volume obtained by attaching a liquid module to an LS-230 type laser diffraction particle size distribution measuring device manufactured by Beckman Coulter, Inc., and setting a particle size of 0.04 to 2000 μm as a measurement range. It was calculated from the standard particle size distribution.

  The volume average particle diameter R1 of the toner T1 as the first developer in this embodiment is 4.0 μm to 6.2 μm (4.0 μm ≦ R ≦ 6.2 μm), so that high image quality can be obtained at the same time. The effects of the embodiment can be obtained. When the volume average particle diameter of the toner exceeds 6.2 μm, roughness occurs on the halftone image, and when it is less than 4.0 μm, the coating on the developing roller cannot be stably performed, so that the image quality is deteriorated.

(Toner regulating member)
The toner regulating member 4 supports a thin plate-like elastic member 42 such as a phosphor bronze plate or a stainless steel plate in a cantilever manner on a support metal plate 41 fixed to the developing container, and the abdominal surface of the opposite portion abuts against the developing roller 3. ing. In this embodiment, an iron plate having a thickness of 1.2 mm is used as a support metal plate, and a phosphor bronze plate having a thickness of 120 μm is bonded to the support metal plate as a thin plate-like elastic member 42. The distance from the cantilever support portion of the thin plate-like elastic member 42 to the contact portion with the developing roller 3, the so-called free length, is 20 mm, and the pushing amount of the developing roller 3 into the thin plate-like elastic member 42 is 1.5 mm. .

(Development roller)
Next, the developing roller 3 as the developer carrying member in this embodiment uses a φ16 mm elastic roller in which a conductive elastic layer 5 mm is formed on a core metal having an outer diameter φ6 mm, and the elastic layer has a volume resistance. Silicone rubber having a value of 10 ⁷ Ωm was used. The resistance value of the developing roller 3 is based on the current value when a DC voltage of 100 V is applied between the core metal of the developing roller 3 and the stainless steel cylindrical member with the stainless steel cylindrical member having an outer diameter of 30 mm and the developing roller 3 in contact with each other. The resistance value of the developing roller 3 was calculated. The measurement environment was 23.0 ° C. and 50% RH.

  The elastic roller surface layer may be provided with a coat layer having a function of imparting charge to the developer. In the present embodiment, the hardness of the elastic layer is set to 45 ° in order to bring the photosensitive drum 1 into elastic contact with stability. Here, the hardness of the developing roller elastic layer was measured using an Asker-C hardness meter manufactured by Kobunshi Keiki Co., Ltd. with a load of 1 kg.

  The arithmetic average roughness Ra as the surface roughness of the developing roller 3 was 1.5. The surface roughness Ra in this example was measured using a surface roughness tester SE-30 manufactured by Kosaka Laboratory Co., Ltd. based on JIS B0601.

(Supply roller)
In the present embodiment, the supply roller 5 is an elastic sponge roller in which a conductive elastic layer having a foamed skeleton structure is formed on a core bar having an outer diameter of 5 mm, and the elastic layer has a volume. A polyurethane foam having a resistance value of 10 ⁷ Ωm was used.

  The supply roller 5 is in contact with the developing roller 3, and supplies toner onto the developing roller 3 with moderate irregularities on the surface of the foam and removes the residual image without being consumed during development. The scraping property of the cell structure is not limited to urethane foam, and rubber or the like obtained by foaming silicone rubber or ethylene propylene diene rubber (EPDM rubber) can be used.

  In this example, the following method was used to measure the hardness of the elastic layer. FIG. 7 is a schematic diagram for explaining a method for measuring the hardness of the elastic layer of the supply roller 5.

  As shown in FIG. 7, in this embodiment, the push-in member 17 includes a cylindrical portion 17a that is in contact with the supply roller 5 and an arm portion 17b that is not in direct contact with the surface of the supply roller. The pressure sensor is connected. The pressure generated when the pushing member 17 was pushed into the supply roller surface was measured.

  Specifically, since the developing roller 3 has an outer diameter of φ16 mm, a pushing member cylindrical portion 17 a having an aluminum column having an outer diameter of φ16 mm and a length of 50 mm was used. Then, the pressure when the center axis of the supply roller 5 and the center axis of the pressing member cylindrical portion 17a are collinear and compressed by 1.0 mm at a speed of 1.0 mm / sec is measured, and the unit length The contact pressure was defined as the supply roller elastic layer / hardness.

  The elastic layer hardness in this example is 0.040 N / mm.

(Development roller / Supply roller)
The overlap amount, that is, the so-called “advance amount” between the surface of the supply roller before incorporating the developing roller and the surface of the developing roller after incorporating the developing roller was 1.0 mm. At this time, the pushing direction is a straight line passing through the central axis of each roller in the cross section as shown in FIG. 1 (a straight line connecting the central axis of each roller in the cross section, a straight line substantially orthogonal to the central axis of the core). The direction was approximately parallel to

  Further, the pressure (contact pressure) generated when the developing roller 3 and the supply roller 5 contact each other was measured by the pushing member 17 in the same manner as the elastic layer / hardness. The difference from the elastic layer hardness measurement is that the pressure per unit length with respect to the actual penetration amount is defined as the contact pressure.

  In this example, the contact pressure at an approach amount of 1.0 mm was set to 0.040 N / mm.

  Here, in this embodiment, toner T2 as a second developer is applied in advance to the surface of the developing roller 3 and the surface of the supply roller 5 when the developing device D is not used. For this purpose, the toner T2 is preferably applied in advance to the surface of the developing roller 3 and the surface of the supply roller 5 before being incorporated into the developing device D.

  FIG. 1B shows the unused developing device D after the developing roller 3 and the supply roller 5 are incorporated into the developing device D. A seal member U is provided in order to suppress leakage of the toner T1 when the developing device D is moved or vibrated when not in use. By removing the seal member U at the start of use, supply of the toner T1 to the developing roller 3 is started.

(Method of applying toner T2 to developing roller and supply roller)
A method of applying the toner T2 to the developing roller 3 or the supply roller 5 before being assembled in the developing device D in this embodiment will be described with reference to FIG.

  FIG. 8 is a diagram for explaining a method of applying the toner T2 to the developing roller 3 or the supply roller 5. In FIG. In order to apply the toner T2 to the developing roller 3 or the supply roller 5, as shown in FIG. 8, a toner container 15b having a rotatable elastic roller 15a and containing the toner T2 is provided.

  As the elastic roller 15a rotates in the rotation direction e, the toner T2 adheres to the surface of the elastic roller 15a. Next, a predetermined pressure 15c is applied to the core of the developing roller 3 or the supply roller 5 and brought into contact with the elastic roller 15a. Thereafter, by rotating the elastic roller 15a in the rotation direction e, the developing roller 3 or the supply roller 5 is driven to rotate in the rotation direction f. The toner T2 was applied to the developing roller 3 or the supply roller 5 by rotating the elastic roller 15a for a predetermined time.

(First developer: Toner T1 production)
The toner T1 composed of the one-component nonmagnetic toner T is prepared by a suspension polymerization method including a binder resin and a charge control agent, and is prepared by adding a fluidizing agent or the like as an external additive. The volume average particle size R1 at this time was 5.8 μm.

  Here, the volume average particle size is a volume standard obtained by attaching a liquid module to a LS-230 type laser diffraction particle size distribution measuring device manufactured by Beckman Coulter, Inc., and measuring a particle size of 0.04 to 2000 μm. The particle size distribution was calculated.

In the toner T1 as the first developer of the present embodiment, a toner having a volume average particle diameter R1 of 4.0 μm or more and 6.2 μm or less can obtain high image quality and at the same time obtain the effects of the present invention. Can do. If the volume average particle diameter of the toner exceeds 6.2 μm, roughness occurs on the halftone image, and if it is less than 4.0 μm, it is difficult to form a stable toner layer on the developing roller, so that the image quality deteriorates.

  The ratio Ra / R1 of the arithmetic average roughness Ra of the developing roller surface to the volume average particle diameter R1 of the toner T1 as the first developer is 0.259.

  Further, the half width was obtained from the volume-based particle size distribution (volume particle size distribution). The full width at half maximum H1 of the toner T1 in this example was 3.0.

  Further, the average circularity of the toner T1 was 0.98.

  The average circularity in this embodiment is used as a simple method for quantitatively expressing the shape of the particles. In this embodiment, a flow type particle image analyzer “FPIA” manufactured by Toa Medical Electronics Co., Ltd. (currently Sysmex) is used. -2100 "is used for measurement. Specifically, the circularity (Ci) of each particle measured for a particle group having a circle-equivalent diameter of 3 μm or more is obtained by the following equation (1), and is further measured by the following equation (2). A value obtained by dividing the sum of the circularity of all particles by the total number of particles (m) is defined as the average circularity ().

・・・式（１）

・・・式（２）

... Formula (1)

... Formula (2)

  If the average circularity of the toner T1 as the first developer used in this embodiment is 0.965 or more, the effects of the present invention can be obtained. If the average circularity is less than 0.965, it is difficult to form a uniform toner coat layer, and it is difficult to obtain a more uniform image.

(Second developer: Toner T2 production)
In the production of the toner T2 as the second developer described above, the toner T2 was produced in the same manner as the toner T1 except that the volume average particle diameter R2 was different. The volume average particle diameter R2 of the toner T2 as the second developer in this embodiment was 6.8 μm, and the half-value width H2 of the volume particle size distribution was 3.4.

  That is, the ratio R2 / R1 of the volume average particle size R2 of the toner T2 to the volume average particle size R1 of the toner T1 is 1.17, and satisfies 1.0 <R2 / R1 ≦ 1.5.

  The ratio H2 / H1 of the half width H2 of the toner T2 to the half width H1 of the toner T1 is 1.13, which satisfies 1.0 <H2 / H1 ≦ 2.0.

When the relationship between the half widths of the toner T1 and the toner T2 used in the present embodiment is H2 / H1 ≦ 2.0, the effect of the present invention can be obtained.

  When H2 / H1> 2.0, the particle size distribution of the toner T2 is significantly wider than that of the toner T1. For this reason, the difference in charge polarity from that of the toner T1 is remarkably increased, so that the effect of suppressing a solid white image defect described later cannot be obtained.

(Applied voltage)
The image forming apparatus A is provided with a first voltage applying unit that applies a voltage to the developing roller 3 and a second voltage applying unit that applies a voltage to the toner regulating member 4. Then, a voltage of −300 V is applied to the developing roller mandrel as the applied voltage Vs (Va) applied to the developing roller 3 by the first voltage applying unit. Further, a voltage of −300 V is applied to the toner regulating member 4 as the applied voltage Vb applied to the developer amount regulating unit by the second voltage applying unit.

  Here, the relationship between Vs and Vb is Vs × Vb> 0 and | Vs | = | Vb |.

  Further, −600 V is applied to the supply roller core metal.

[Example 2]
The second embodiment of the present invention basically conforms to the first embodiment, but differs in the following points.

  A voltage of −500 V is applied to the toner regulating member 4 as the applied voltage Vb to the developer amount regulating means.

  Therefore, the relationship between Vs and Vb is Vs × Vb> 0 and | Vs | <| Vb |.

[Example 3]
The third embodiment of the present invention basically conforms to the first embodiment, but differs in the following points.

  The difference is that the arithmetic surface roughness Ra of the surface of the developing roller is 0.1.

  Therefore, the ratio Ra / R1 of the arithmetic average roughness Ra of the developing roller surface to the volume average particle diameter R1 of the toner T1 as the first developer is 0.017.

[Example 4]
The fourth embodiment of the present invention basically conforms to the third embodiment, but differs in the following points.

  A voltage of −500 V is applied to the toner regulating member 4 as the applied voltage Vb to the developer amount regulating means.

  Therefore, the relationship between Vs and Vb is Vs × Vb> 0 and | Vs | <| Vb |.

  That is, it means that the voltage applied to the toner regulating member 4 is applied in the direction in which the toner is pressed against the surface of the developing roller.

[Comparative Example 1]
Comparative Example 1 basically conforms to Example 1, but differs in the following points.

The same toner T2 as the first developer was used as the toner T2 as the second developer. That is, in this comparative example, the volume average particle diameter R2 of the toner T2 is 5.8, the average circularity is 0.98, and the ratio R2 of the volume average particle diameter R2 of the toner T2 to the volume average particle diameter R1 of the toner T1. / R1 is 1.0.

[Comparative Example 2]
Comparative Example 2 is basically the same as Comparative Example 1, but differs in the following points.

  A voltage of −500 V is applied to the toner regulating member 4 as the applied voltage Vb to the developer amount regulating means.

  Therefore, the relationship between Vs and Vb is Vs × Vb> 0 and | Vs | <| Vb |.

[Comparative Example 3]
Comparative Example 3 is basically the same as Comparative Example 1, but differs in the following points.

  The difference is that the arithmetic surface roughness Ra of the surface of the developing roller is 0.1.

  Therefore, the ratio Ra / R1 of the arithmetic average roughness Ra of the developing roller surface to the volume average particle diameter R1 of the toner T1 as the first developer is 0.017.

[Comparative Example 4]
Comparative Example 4 is basically the same as Comparative Example 3, but differs in the following points.

  A voltage of −500 V is applied to the toner regulating member 4 as the applied voltage Vb to the developer amount regulating means.

  Therefore, the relationship between Vs and Vb is Vs × Vb> 0 and | Vs | <| Vb |.

[Comparative Example 5]
Comparative Example 5 is basically the same as Example 1, but differs in the following points.

  The difference is that the half-value width H2 of the particle size distribution of the toner T2 as the second developer is 2.5, and H2 / H1 = 0.83.

[Comparative Example 6]
Comparative Example 6 basically conforms to Example 4, but differs in the following points.

  The difference is that the half-value width H2 of the particle size distribution of the toner T2 as the second developer is 2.5, and H2 / H1 = 0.83.

[Comparative Example 7]
Comparative Example 7 is basically the same as Comparative Example 1, but differs in the following points.

  The volume average particle diameter R1 of the toner T1 as the first developer is 7.5 μm. That is, R2 / R1 = 1.0 and Ra / R1 = 0.4.

[Evaluation Methods for Examples and Comparative Examples]
The image evaluation for examining the difference between the example and the comparative example will be described below.

a) Solid white image defect evaluation at the initial stage of printing Image evaluation was performed by visually evaluating image defects generated in a developing roller cycle in solid white and in a halftone image. The development cycle was accurately calculated in consideration of the process speed and the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3, and image defects having the same cycle were extracted and evaluated. In the solid white image, the size of the image defect is about 1.0 to 5.0 mm, and the partial optical density is about 0.3 to 1. Further, even in a halftone image, the size of the image defect is an image defect that causes a density difference comparable to that in a solid white image. The evaluation can be clearly discriminated with and without defects, and was evaluated according to the following criteria.
XX: Solid white image and halftone image, with image defect, and defect size exceeds 3.0 mm.
X: Solid white image and halftone image, with image defects, and defect size of 3.0 mm or less.
Δ: Solid white image has no image defect, and halftone image has image defect.
A: Solid white image and halftone image with no image defect.

  Evaluation was made by leaving an unused developing device at 15.0 ° C. and 10% Rh for 240 hours, printing five solid white images immediately after opening the toner seal, and one halftone image. The solid white image and the halftone image were evaluated.

  In each example printer, image recording (image formation) was performed using a 600 dpi laser scanner. In this evaluation, a halftone image means a striped pattern in which one line in the main scanning direction is recorded and then four lines are not recorded, and expresses a halftone density as a whole.

b) Uniformity Evaluation of Image Density Image evaluation evaluated the uniformity by outputting a solid black image and a halftone image. When the uniformity is lowered, a thin spot 1 having a sandy (0.1 mm or less) density is generated in a uniform image. When further deteriorated, a spot 2 on an ellipse extending in the rotation direction of the developing roller is generated. The presence or absence of the spots was visually observed, and the image density uniformity was evaluated according to the following criteria.
X: Sand-like spots 1 and elliptical spots 2 are recognized in the solid black image and the halftone image.
Δ: Sand-like spots 1 are recognized in the solid black image and the halftone image.
○: Sand-like spots 1 are recognized in either the solid black image or the halftone image.
A: Sandy spot 1 is not recognized in either the solid black image or the halftone image.

  Evaluation of image uniformity was performed after printing 1000 sheets at an evaluation environment of 15.0 ° C., 10% Rh. The printing test was performed by continuously passing a horizontal line of recorded images having an image ratio of 5%.

  In each example printer, an image was recorded using a 600 dpi laser scanner. In this evaluation, the halftone image means a striped pattern in which one line in the main scanning direction is recorded and then four lines are not recorded, and the halftone density is expressed as a whole.

c) Fog evaluation after endurance Fog is an image defect that appears as a background stain due to slight development of toner in a white portion (unexposed portion) that is not originally printed.

The amount of fog is measured by measuring the optical reflectance with a green filter with an optical reflectance measuring machine (TC-6DS, manufactured by Tokyo Electric Decoration Co., Ltd.) and subtracting from the reflectance of only the recording material to obtain the amount of fog as the amount of fog. evaluated. The fog amount was measured at 10 or more points on the recording material, and the average value was obtained.
XX: The fog amount exceeds 2%.
X: The fog amount is less than 1 to 2%.
Δ: The fogging amount is less than 0.5 to 1%.
A: The fog amount is less than 0.5%.

The fog evaluation was performed after printing 20,000 sheets at a test environment of 30 ° C. and 80% Rh. The print test
A horizontal line recorded image having an image ratio of 5% was continuously fed. In addition, when other image defects described below occur, the measurement was performed while avoiding the location, and consideration was given so that the fog could be evaluated purely.

d) Fog characteristic evaluation when the remaining amount of toner is reduced By repeating the printing test, the toner accumulated in the developing device is reduced, the evaluation image of the horizontal line is gradually thinned, and is sometimes interrupted. Thus, the fog characteristic when the remaining amount of toner decreased was separately evaluated.

  In the print test, when a horizontal line image defect as described above occurs, fog evaluation is performed, and then the developing device is removed from the image forming device and shaken to remove toner in the developing device. The image is sent to the device and attached to the device again to evaluate fog. In these image evaluations, the same fog evaluation as described above is performed, and the worst (large) result is used as the fog evaluation of the main evaluation.

Table 1 shows the evaluation results of Examples 1 to 4 and Comparative Examples 1 to 7.

[Advantages over conventional technology]
First, the superiority of the present invention will be described by comparing the comparative example 7 as the prior art with the example 1.

  In Comparative Example 7, the surface roughness of the developing roller with respect to the average particle diameter of the toner is very large. Therefore, the toner coat layer is likely to vary depending on the roughness of the developing roller. As a result, speckles extending in the direction of the developing roller are generated, and the uniformity of the image density is poor. Further, since the roughness of the developing roller is very large, locally high stress is applied to the toner due to the pressing and rubbing of the developing roller and the photosensitive drum or the developing roller and the supply roller. As a result, it is easy to promote toner deterioration, an increase in the fog amount after durability, and a durable ghost image defect occur.

  For this reason, when the developing device is shaken when the toner runs out, the toner having little deterioration and the toner having remarkably deteriorated are mixed in the developing container. Since the charge imparting property of the toner is different, a toner having a reverse polarity is easily generated. As a result, fogging at the time of running out of toner is worsened.

  On the other hand, in Example 1 of the present invention, the image density uniformity can be improved. Further, although the reason for suppression will be described later, fogging at the time of running out of toner can also be suppressed. That is, it is possible to obtain an image with high image quality and suppressed image defects from the initial printing to the time when the number of stamps is increased.

[Advantages over comparative technology]
Next, the advantages of the present invention will be described by comparing Examples 1 to 4 and Comparative Examples 1 to 7.

<A) Solid white image defect evaluation result, and b) Image density uniformity evaluation result>
As described above, in Comparative Example 7, since the volume average particle size R1 of the toner T1 is as large as 7.5 μm and the arithmetic surface roughness Ra of the developing roller surface is 3.0 μm, Ra / R1 = 0. 4 and big. For this reason, the uniformity of the toner layer is lowered, and the uniformity of the image density is also lowered.

  On the other hand, in Example 1 and Comparative Example 1, the toner T1 as the first developer has a volume average particle size R1 of 5.8 μm and an arithmetic surface roughness Ra of 1.5 μm on the surface of the developing roller. Improves. As a result, the uniformity of image density is also improved.

  Further, Example 2 and Comparative Example 2 are examples in which, with respect to Example 1 and Comparative Example 1, the voltage applied to the toner regulating member 4 is applied in the direction in which the toner is pressed against the surface of the developing roller. Therefore, it is considered that toner layer formation after regulation can be performed uniformly. In addition, since the toner charge imparting by the toner regulating member 4 is stably performed, it is considered that the uniformity of the charge amount of the toner in the toner layer on the developing roller is also improved. As a result, the uniformity of image density is further improved.

  Further, Example 3 and Comparative Example 3 are examples in which the arithmetic surface roughness Ra of the developing roller 3 is set to 0.1 with respect to Example 1 and Comparative Example 1. For this reason, the influence of the roughness of the developing roller surface is remarkably reduced when the toner layer is formed, so that a more stable toner layer can be formed.

  Further, the adhesion force between the toner and the developing roller is dominated by the electrical restraining force because the surface of the developing roller has a small roughness. Therefore, when the toner is transferred by an electric field in the developing unit, more uniform transfer can be performed. In addition, since the surface roughness is small, the disturbance of the toner layer due to the roughness of the developing roller 3 is also reduced when the developing roller 3 and the photosensitive drum are rubbed. As a result, the image density uniformity is improved.

  And Example 4 and Comparative Example 4 are remarkably excellent in image density uniformity. Example 4 and Comparative Example 4 are examples in which Ra / R1 = 0.02 and the voltage is applied to the toner regulating member 4 in the direction in which the toner is pressed against the developing roller 3. Therefore, as described above, a uniform toner layer is formed while forming a state where the toner is more electrically restrained on the surface of the developing roller. As a result, it is considered that the image density uniformity is remarkably improved.

  From the above, in order to improve the uniform toner layer and density uniformity, it is considered that the electric force is dominant in the adhesion force between the developing roller surface and the toner.

  However, in Comparative Examples 1 to 4, a solid white image defect occurs as the image density uniformity improves, that is, as the electric force becomes dominant.

  First, the approximate generation mechanism of a solid white image defect is considered as follows. Here, FIG. 1B shows an unused developing device as described above.

  After the seal member U is removed when the developing device is used, the agitation member 11 conveys the toner T1 to the vicinity of the supply roller. Thereafter, the toner T1 adhering to the surface of the supply roller is supplied to the development roller 3 by sliding between the development roller 3 and the supply roller 5. However, immediately after the seal member U is removed, that is, before the toner T1 reaches the supply roller 5 or the surface of the developing roller, the developing roller 3 rotates. Meanwhile, the chance that the toner T2 previously applied to the surface of the developing roller or the surface of the supply roller passes through the toner regulating member 4 increases. As a result, charge is excessively applied to the toner T2, and the toner T2 adheres firmly to the surface of the developing roller due to the electrical restraining force. For this reason, the toner T <b> 2 is not easily separated from the surface of the developing roller even after a peeling process by rubbing the supply roller 5. Thereafter, when the toner T1 reaches the developing roller 3 through the surface of the supply roller, the toner T1 passes through the toner regulating member 4 and is given an electric charge. After that, if a charge amount equivalent to that of the toner T2 firmly adhered to the surface of the developing roller can be obtained, the toner T1 has an electric adhesion force, and the replacement with the toner T2 is continuously performed on the surface of the developing roller. Can be done automatically. As a result, no solid white image defect occurs.

  However, when the toner T2 has an adhesive force that is significantly higher than the electric adhesive force due to the charge imparted to the toner T1, it is difficult to replace the toner T1. The surface of the developing roller to which the toner T2 is attached is close to a state having a particle size R1 roughness of the toner T1. For this reason, the physical conveyance force of the toner T1 by the surface of the developing roller increases, and at the same time, an excessive amount of toner is conveyed, so that the charge imparting property to the toner T1 is lowered even when passing through the toner regulating member 4. That is, the toner T1 that has not obtained an appropriate charge is conveyed to the developing unit.

  As a result, in the contact development in which the photosensitive drum 1 and the developing roller 3 are in contact with each other, it is difficult to electrically control the toner T1 having an insufficient amount of charge. Therefore, a spot of about 0.5 to 2.0 mm is formed on the solid white image. Occurs in the developing roller cycle. That is, a solid white image defect occurs. When the solid white image defect is slight, spot density unevenness of about 0.5 to 2.0 mm occurs in the halftone image in the developing roller cycle.

  From the above, it is considered that the solid white image defect is more likely to occur as the electric force becomes dominant as the adhesion force between the developing roller 3 and the toner.

  However, as described above, in order to improve the image density uniformity, electrical power needs to be dominant, and the two problems of improving the image density uniformity and suppressing the solid white image defect are contradictory problems. It is difficult to achieve both.

  Therefore, in Comparative Examples 1 to 4, the solid white image defect deteriorates as the image density uniformity improves. In particular, Comparative Example 4 has very good image density uniformity, but the solid white image defect is very bad.

  On the other hand, Examples 1 to 4 of the present invention remarkably suppress solid white image defects regardless of the evaluation result of the image density uniformity. That is, it is considered that the effect of suppressing the solid white image defect can be obtained even when the electrical dominance is increased. In Examples 1 to 4 of the present invention, the relationship between the volume average particle size R1 of the toner T1 and the volume average particle size R2 of the toner T2 is R2 / R1> 1.0. The magnitude of the mirror force acting between the toner and the developing roller is proportional to the square of the charge amount of the toner particles, and inversely proportional to the square of the toner particle size. Therefore, when the toner particle size is large, the adhesion can be weakened due to the effect of the particle size.

Further, when the toner particle size is large, the number of times one toner comes into contact with the toner regulating member 4 is decreased, so that the charge imparting property due to frictional charging, that is, the amount of charge obtained by the toner particles is decreased. That is, the adhesion force of the toner T2 to the developing roller 3 can be significantly reduced. Therefore, an increase in the adhesion force between the toner T2 on the developing roller and the developing roller surface before the toner T1 reaches the developing roller surface can be suppressed.

  As a result, it is possible to suppress the specific toner T2 from firmly adhering to the developing roller, and thus it is possible to remarkably suppress the solid white image defect.

  As described above, in the embodiment of the present invention, even when a toner having a small particle size is used for high image quality, the relationship of R2 / R1> 1.0 is satisfied, so that solid white image defects are remarkably increased. Can be suppressed. Further, it is possible to satisfy both the problems of improving the uniformity of image density and contradicting the suppression of solid white image defects.

  However, in Comparative Examples 5 and 6, a solid white image defect occurs even though R2 / R1> 1.0. The reason is considered that the ratio H2 / H1 of the half width H2 of the toner T2 to the half width H1 of the toner T1 is 0.83. That is, the particle size distribution of the toner T2 is sharper than the particle size distribution of the toner T1. Since the particle sizes of the toners T1 and T2 have a relationship of R2 / R1> 1.0, it is considered that strong adhesion to the developing roller 3 is suppressed.

  However, when the toner T1 starts to be supplied to the developing roller 3, it is considered that the toner T1 has priority over the toner T2 forming the toner layer. The reason is that since the particle size distribution of the toner T2 is sharp, any toner T2 is easily separated from the developing roller 3, and conversely, the toner T1 having a small particle size is easily attached to the developing roller 3. The toner T2 is rapidly changed to the toner T1. That is, as in Comparative Example 1, it is considered that the toner T1 is close to being applied in advance. As a result, a solid white image defect occurs.

  On the other hand, in Examples 1 to 4, since H2 / H1> 1.0, when the toner T1 reaches the developing roller, the toner that is easily separated from the developing roller 3 and the toner that is slightly difficult to separate form a toner layer. Conceivable. As a result, the toner layer on the developing roller is gradually replaced from the toner T2 to the toner T1, and the generation of the toner firmly attached to the developing roller 3 is suppressed.

  As a result, it is considered that the solid white image defect is remarkably suppressed.

  As described above, according to the embodiment of the present invention, the ratio R2 / R1 of the average volume particle diameter of the toner is R2 / R1> 1.0, and the ratio H2 / H1 of the half width of the particle size distribution of the toner is H2. Since /H1>1.0, solid white image defects can be remarkably suppressed.

<A) Solid white image defect evaluation result, and c) Fog evaluation result after durability>
First, the cause of fogging after endurance will be described.

  The toner in the developing unit is subjected to high stress due to the pressing and sliding of the photosensitive drum 1 and the developing roller 3. In addition, the toner in the supply unit is subjected to high stress due to the pressing and rubbing of the developing roller 3 and the supply roller 5. Therefore, external additives such as silica coated on the toner are likely to be embedded in the toner or released from the toner. As a result, the chargeability of the toner at the initial printing number is significantly lowered. In other words, since the toner coat layer with a small amount of charge is formed, the toner with a small amount of charge has a weak electrical restraining force. As a result, the toner on the developing roller has a lower electrical restraining force, so that when the toner comes into contact with the photosensitive drum 1, the toner tends to transfer onto the photosensitive drum and the amount of fog increases.

  Further, it is considered that the external additive has an action of reducing the adhesion force between the toner and the object by interposing between the toner and the object when they are in contact with each other. Then, the embedding or releasing of the toner increases the adhesion between the toner and the object. For this reason, the adhesion force of the toner to the photosensitive drum 1 is remarkably increased, so that the toner is more easily transferred onto the photosensitive drum.

  Compared to Example 1, Example 4 is good without any increase in the amount of fogging after durability. The reason is that since the voltage is applied to the toner regulating member 4 in the direction in which the toner is pressed against the developing roller 3, the electrical adhesion force of the toner to the developing roller 3 is dominant as described in the previous section. Become. The electrical adhesion force of the toner to the developing roller 3 is also dominant because Ra / R1, which is the ratio of the arithmetic surface roughness of the developing roller surface to the volume average particle diameter of the toner, is as small as 0.02. Become. As a result, it is possible to suppress a decrease in charge imparting property of the toner after the endurance.

  Further, when the surface roughness of the developing roller with respect to the toner particle size is small, the toner is stressed on the developing roller during pressing and rubbing between the developing roller 3 and the photosensitive drum 1 or between the developing roller 3 and the supply roller 5. It is thought that it is easy to move in the decreasing direction. That is, it is possible to suppress the occurrence of specific toner that has been subjected to high local stress and significantly deteriorated, and the durability fogging.

  Further, in Examples 2 and 3, the increase in the amount of fog is small compared to Example 1. In the second embodiment, a voltage is applied to the toner regulating member 4 in the direction in which the toner is pressed against the developing roller 3, and in the third embodiment, Ra is the ratio of the arithmetic surface roughness of the developing roller surface to the volume average particle diameter of the toner. / R1 is as small as 0.02. For this reason, the electric adhesion force of the toner to the developing roller 3 becomes dominant. As a result, increase in durability fog is suppressed.

  That is, in order to suppress the durability fogging, it is necessary to increase the electric adhesion force of the toner to the developing roller 3 as well as the improvement of the image density uniformity. That is, it is considered that the suppression of durable fog and the solid white image defect are contradictory issues. This can also be seen from the fact that the solid white image defect deteriorates with the suppression of the durable fog of Comparative Examples 1 to 4. On the other hand, in Examples 2 to 4, solid white image defects are suppressed simultaneously with the suppression of durable fog.

  As described above, in the embodiment of the present invention, it is possible to simultaneously suppress the contradictory problems of suppression of durable fog and suppression of solid white image defects.

<D) Result of fogging evaluation when toner runs out>
First, factors that cause fog evaluation when toner runs out will be described.

  The reason for this is that a toner with little deterioration and a deteriorated toner are mixed when the cartridge is shaken, and the deteriorated toner whose charge imparting property is lowered due to the difference in polarity causes a further decrease in charge imparting property, or the charge imparting reverse polarity. Therefore, the amount of fogging is considered to increase actively. In Examples 1 to 4 of the present invention, the increase in fog is remarkably suppressed even when the toner runs out.

  On the other hand, as in Comparative Example 4, there is little deterioration of the toner, and the amount of fog when the toner runs out increases despite the fact that the electrical adhesion of the toner to the surface of the developing roller is dominant. The reason is not clear, but it is thought as follows.

  Since the toner T1 that is the first developer has a toner particle size that is easy to consume, the particle size of the toner in the second half of the endurance is broader in particle size distribution and coarsened in the average particle size than in the first half of the endurance. Conceivable. In addition, it is considered that the toner T1 in the latter half of the durability is further deteriorated compared with the first half of the durability.

  Therefore, it is considered that the charge imparting property of the toner in the latter half of the durability is remarkably lowered as compared with the first half of the durability. In particular, when a toner having a high average circularity and a small particle size is used as in the embodiment of the present invention, the change in the properties of the toner in the first half of the durability and the latter half of the durability causes a great difference in chargeability.

  In Comparative Examples 1 to 4, the toner T2 previously applied to the supply roller 5 is the same as the toner T1 in the developing container. Therefore, it is considered that the difference between the toner particle size in the developing container in the latter half of the durability and the toner T2 is large and the charging property is also different. In addition, it is considered that the toner T2 applied to the supply roller 5 maintains an average particle size comparable to that of the first half of the durability in the second half of the durability. For this reason, when the developing device is shaken in a state where the amount of toner in the developing device is small, such as when the toner runs out, the toner T2 and the highly deteriorated toner T1 are easily mixed. That is, toners having significantly different properties are mixed, and toner that cannot obtain a sufficient amount of charge is generated. As a result, it is considered that the amount of fogging when the toner runs out is increased.

  On the other hand, Embodiments 1 to 4 of the present invention can remarkably suppress the amount of fog even when the toner runs out. The reason is considered to be that the particle diameter R2 of the toner T2 as the second developer previously applied on the supply roller is larger than the particle diameter R1 of the toner T1 in the initial developing container. That is, as the durability progresses, the particle size of the toner T1 in the developing container is broadened in distribution and the average particle size is increased. However, the toner T2 has a relationship of R2 / R1> 1.0 in advance. Therefore, the difference in toner chargeability is small. As a result, even if mixing is performed by hand shaking, fog does not occur.

  However, in Comparative Examples 5 and 6, although the toner particle size ratio is R2 / R1> 1.0, the amount of fog when the toner runs out increases. The reason is considered that the particle size distribution of the toner T2 is sharper than the particle size distribution of the toner T1 in the early stage of durability. When the toner having a broad particle size distribution in the latter half of the durability and the toner T2 having a sharp particle size distribution are mixed, it is considered that the polarity difference in charge imparting property increases as in the case where the particle size difference is large. As a result, the amount of fog when the toner runs out increases.

  As described above, according to the embodiment of the present invention, the toner out-of-toner can be obtained by setting the volume average particle size ratio R2 / R1> 1.0 and the particle size distribution ratio H2 / H1> 1.0. Time fog can be significantly suppressed.

[Relationship between the particle diameters R1, R2 of the toners T1, T2 and the arithmetic surface roughness Ra of the developing roller]
Hereinafter, the relationship between the particle diameters R1 and R2 of the toners T1 and T2 and the arithmetic surface roughness Ra of the developing roller 3 will be described. In particular, Examples 5 to 14 and Comparative Examples 8 to 10 will be described below as an example under the condition of | Vb |> | Vs | in which electrical adhesion is dominant.

[Examples 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
The present embodiment basically conforms to the fourth embodiment, but differs in the following points.

  The volume average particle diameter R1 of the toner T1 is 5.5, 5.8, 5.8, 5.5, 5.5, respectively, in Examples 5, 6, 7, 8, 9, 10, 11, 12, 13, and 14. The difference is 5, 5.5, 5.8, 5.5, 6.2, and 5.5 μm.

  Further, the volume average particle diameter R2 of the toner T2 is 8.0, 6.4, 6.4, 5.8, and Examples 5, 6, 7, 8, 9, 10, 11, 12, 13, and 14, respectively. 5.8, 8.2, 6.0, 5.8, 7.0, 8.0 μm.

  Further, the arithmetic surface roughness Ra of the developing roller surface is 0.2, 0.2, 0.1, 0.1 in Examples 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, respectively. , 0.1, 0.5, 0.6, 0.3, 0.8, and 0.8 μm. The ratio Ra / R1 of the arithmetic average roughness of the developing roller surface to the volume average particle diameter of the toner T1 at that time is 0.040, 0.038, 0.017, 0.025, 0.009, and 0.098, respectively. , 0.100, 0.045, 0.129, 0.145.

  R2 / R1 is 1.45, 1.10, 1.10, 1.05, 1.05, 1 in Examples 5, 6, 7, 8, 9, 10, 11, 12, 13, and 14, respectively. .49, 1.03, 1.05, 1.13, 1.45. Here, R2 / R1 is a ratio of the volume average particle diameter R2 of the toner T2 to the volume average particle diameter R1 of the toner T1.

[Comparative Examples 8, 9, 10, 11]
This comparative example basically conforms to Example 4, but differs in the following points.

  The volume average particle diameter R1 of the toner T1 is different from Comparative Examples 8, 9, 10, and 11 in that it is 5.8, 5.5, 5.8, and 5.5 μm, respectively.

  Further, the volume average particle diameter R2 of the toner T2 is different from Comparative Examples 8, 9, 10, and 11 in that they are 5.8, 5.8, 8.5, and 9.0 μm, respectively.

  Further, the arithmetic surface roughness Ra of the developing roller surface is different from that of Comparative Examples 8, 9, 10, and 11 in 0.8, 0.4, 0.7, and 0.1 μm, respectively. The ratio Ra / R1 of the arithmetic average roughness of the developing roller surface to the volume average particle diameter of the toner T1 at that time is 0.138, 0.073, 0.121, 0. 018.

  The ratio R2 / R1 of the volume average particle diameter R2 of the toner T2 to the volume average particle diameter R1 of the toner T1 is 1.00, 1.55, 1.55,. 00.

(Evaluation methods)
Image evaluation was performed for a) solid white image defect and b) image density uniformity among the evaluation items described above. The evaluation method and evaluation criteria were the same as described above.

(Evaluation results)
In Table 2, the evaluation result of Examples 4-14 and Comparative Examples 8-11 is shown.

<B) Image density uniformity evaluation result>
First, the results of the image density uniformity evaluation are shown in FIG.
In Examples 13 and 14, and Comparative Examples 8 and 10, the image uniformity is slightly poor. On the other hand, Examples 10 and 11 where Ra / R1 ≦ 0.10 (the arithmetic surface roughness Ra of the developing roller surface is 0.10 times or less than the volume average particle diameter R1 of the toner T1) have uniformity. It improves. The reason is that the surface roughness of the developing roller relative to the toner particle diameter is sufficiently small as Ra / R1 ≦ 0.1, so that the variation of the toner coat layer due to the roughness of the developing roller surface is small. As a result, fluctuations during the formation of a uniform toner coat layer and fluctuations in development efficiency at the development portion are remarkably suppressed, so that image uniformity is improved. On the other hand, in Examples 13 and 14 and Comparative Examples 8 and 10, since the surface roughness of the developing roller 3 is slightly large with respect to the average particle diameter of Ra / R1> 0.1 and the toner, the toner due to the surface roughness of the developing roller It is considered that the variation of the coating layer becomes large and the uniformity of the image is deteriorated.

In Examples 4 to 9, 12 and Comparative Example 11, Ra / R1 ≦ 0.04 (the arithmetic surface roughness Ra of the developing roller surface is 0.04 times or less than the volume average particle diameter R1 of the toner T1. ) And the surface roughness of the developing roller with respect to the toner particle size are sufficiently small, so that uniformity is further improved. The reason is considered to be that the uniformity of the toner coat layer is further improved by setting Ra / R1 ≦ 0.04 as described above.

  As described above, in the embodiment of the present invention, in order to improve the uniformity of the toner coat layer and improve the uniformity of the image, it is preferable to satisfy Ra / R1 ≦ 0.1. More preferably, ≦ 0.04.

<A) Solid white image defect evaluation result>
Next, the solid white image defect evaluation result is shown in FIG.

  Comparative Example 8 and Comparative Example 11 have poor solid white image defects. On the other hand, Examples 11-13 which are R2 / R1> 1.0 are favorable. In Comparative Examples 8 and 11, since R2 / R1 = 1.0, it is considered that the toner T1 forming the toner layer is not smoothly replaced before the toner T1 reaches the surface of the developing roller. It is done. That is, before the toner T1 reaches the surface of the developing roller, the toner T2 easily passes through the toner regulating member many times, so that the charge amount of the toner T2 increases and the electrical adhesion increases. As a result, replacement with the toner T1 becomes difficult, and a solid white image defect occurs.

  On the other hand, in Examples 11 to 13, since R2 / R1> 1.0, the adhesion force of the toner T2 coated in advance is considered to be smaller than that of the toner T1. As a result, smooth replacement can be performed and solid white image defects can be suppressed.

  However, in Examples 8 and 9, a slight solid white image defect occurs even though R2 / R1> 1.0. The reason is considered to be Ra / R1 ≦ 0.04 and R2 / R1 <1.1. Since R2 / R1 <1.1, it is considered that the difference in particle size between the toner T1 and the toner T2 is small and the difference in adhesion to the surface of the developing roller is also small. In addition, since Ra / R1 ≦ 0.04, the roughness of the developing roller surface with respect to the toner T1 and the toner T2 is small, and the electric adhesion force becomes more dominant. As a result, the toner T2 adheres firmly and cannot be sufficiently replaced with the toner T1, resulting in a slight solid white image defect.

  On the other hand, Examples 4, 6, and 7 suppress solid white image defects despite Ra / R1 ≦ 0.04. The reason is considered to be because R2 / R1 ≧ 1.1. That is, even if the electrical adhesion force such as Ra / R1 becomes dominant, since R2 / R1 ≧ 1.1, the adhesion force of the toner T2 does not increase significantly. As a result, solid white image defects are remarkably suppressed.

  As described above, in order to suppress the solid white image defect, it is preferable that R2 / R1> 1.0, and in a region where the electrical adhesive force is dominant such as Ra / R1 ≦ 0.04. Is more preferably R2 / R1 ≧ 1.1.

  In Comparative Examples 9 and 10, a solid white image defect occurs even though R2 / R1> 1.1. On the other hand, Examples 5, 10, and 14 where R2 / R1 ≦ 1.5 remarkably suppress the solid white image defect. When R2 / R1> 1.5, the adhesion force of the toner T2 is significantly smaller than that of the toner T1, and thus Comparative Examples 9 and 10 are considered to cause solid white image defects.

  This is because if the adhesion force of the toner T2 is very small compared to the adhesion force of the toner T1, when the toner T1 reaches the surface of the developing roller, the toner T2 is easily replaced with the toner T2. Further, when the toner T2 and the toner T1 having higher charge imparting property than the toner T2 coexist, charge imparting of the toner T1 is accelerated. As a result, a strong adhesion of the toner T1 to the developing roller 3 is generated. As a result, a solid white image defect occurs.

  As described above, in the embodiment of the present invention, solid white image defects can be suppressed by 1.0 <R2 / R1 ≦ 1.5. Further, even in a state where electrical adhesion force is dominant such as Ra / R1 ≦ 0.04, 1.1 ≦ R2 / R1 ≦ 1.5 significantly suppresses solid white image defects. can do.

<A) Solid white image defect, b) Comprehensive evaluation result of image density uniformity>
FIG. 6 shows a comprehensive evaluation result of a) solid white image defect and b) image density uniformity.

  In the embodiment of the present invention, in order to suppress the solid white image defect while maintaining the image density uniformity, it is preferable that 1.0 <R2 / R1 ≦ 1.5. In order to improve further, it is preferable that Ra / R1 ≦ 0.10. Furthermore, in order to have good image density uniformity, it is preferable that Ra / R1 ≦ 0.10 and 1.0 <R2 / R1 ≦ 1.5.

  As described above, according to the embodiment of the present invention, a high-quality image can be obtained by using a toner having a small particle size and high sphericity, and a toner coat layer having a uniform developer can be printed. Regardless of the number of sheets, it can be obtained stably. Therefore, it is possible to obtain high-quality and good images over time (over a long period of time). In particular, it is possible to satisfy both the problems of image density uniformity and solid white image defect. In addition, fogging that occurs when the toner runs out can be suppressed.

1 is a schematic diagram of a developing device in Embodiment 1. FIG. 1 is a schematic diagram of an image forming apparatus in an embodiment. FIG. 2 is a schematic diagram of a process cartridge according to the embodiment. The figure which shows a solid white image defect evaluation result. The figure which shows an image density uniformity evaluation result. The figure which shows a solid white image defect and image density uniformity comprehensive evaluation result. Schematic for demonstrating the method to measure the hardness of a supply roller elastic layer. Schematic for demonstrating the toner application method to a developing roller or a supply roller. Schematic of the developing device in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3 Developing roller 4 Toner control member 5 Supply roller A Image forming apparatus B Process cartridge D Developing apparatus F Developer container T1 Toner (first developer)
T2 toner (second developer)

Claims (7)

A developer carrying member carrying the developer;
A developer container containing a developer;
Developer supply means for supplying the developer contained in the developer container to the developer carrier;
A developer amount regulating means for regulating the developer carried on the developer carrying body;
With
In the developing device in which the developer carrying member is provided so as to come into contact with the developing member, and the developing member is developed with the developer,
A first developer housed in the developer container, having a volume average particle size of 4.0 μm or more and 6.2 μm or less, and an average circularity of 0.965 or more;
A second developer pre-applied to the surface of the developer carrier and the surface of the developer supply means in a state where the developing device is not used;
With
When the volume average particle size of the first developer is R1, and the volume average particle size of the second developer is R2, the relationship between R1 and R2 is
1.0 <R2 / R1 ≦ 1.5
The filling,
When the half-value width of the volume particle size distribution of the first developer is H1, and the half-value width of the volume particle size distribution of the second developer is H2, the relationship between H1 and H2 is
1.0 <H2 / H1 ≦ 2.0
A developing device characterized by satisfying the above.   2. The developing device according to claim 1, wherein an arithmetic average roughness Ra of a surface of the developer carrying member is 0.10 times or less with respect to a volume average particle diameter R <b> 1 of the first developer. The arithmetic average roughness Ra of the surface of the developer carrying member is 0.04 times or less with respect to the volume average particle diameter R1 of the first developer,
The relationship between R1 and R2 is
1.1 ≦ R2 / R1 ≦ 1.5
The developing device according to claim 1, wherein:   A process cartridge comprising the developing device according to claim 1, wherein the process cartridge is detachably attached to the image forming apparatus. An image carrier;
The developing device according to any one of claims 1 to 3, which performs a developing action on the image carrier;
An image forming apparatus comprising:   An image forming apparatus comprising the process cartridge according to claim 4 detachably. First voltage applying means for applying a voltage to the developer carrying member;
Second voltage applying means for applying a voltage to the developer amount regulating means;
With
When the applied voltage applied to the developer carrying member by the first voltage applying unit is Va and the applied voltage applied to the developer amount regulating unit by the second voltage applying unit is Vb, Va is The relationship with Vb is
Vb × Va> 0 and | Vb |> | Va |
The image forming apparatus according to claim 5, wherein:

Images