JP2010139850A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device where, even if a carrier has a small diameter, a toner is recovered from a toner layer on a development roller, and a satisfactory image is obtained over a long period without generating the unevenness of solid images and ghost images, and also without causing a developer leak, and also to provide an image forming apparatus using the developing device. <P>SOLUTION: The developing device comprises: a photosensitive drum forming an electrostatic latent image; a toner carrier freely rotatably supported so as to face the photosensitive drum and carrying a toner to the outer circumferential part; and a developer carrier incorporating a magnetic member, which is freely rotatably supported so as to face the toner carrier and holds a two-component developer composed of a toner and a carrier. In the developing device, there is a gap of a prescribed distance between the toner carrier and the developer carrier, and carrier volume abundance in the gap is 16 to 24%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing device adopting a touch-down developing method as a developing method, and an image forming apparatus to which the developing device is applied.

  As a developing method in an electrophotographic image forming apparatus, a one-component developing method and a two-component developing method are known. Also known is a touch-down development system (hybrid development system) that combines the characteristics of a one-component development system (high image quality) and the characteristics of a two-component development system (long life) (see Patent Document 1).

  In the touchdown development method, a two-component developer containing toner and carrier is carried on the surface of a magnetic roller (developer carrier), and only the toner is developed from the two-component developer carried on the surface of the magnetic roller. The toner layer is transferred to the surface of the toner carrier to form a toner layer on the surface of the developing roller, and the toner is transferred from the toner layer to the surface of the photosensitive drum on which the electrostatic latent image is formed. This is a method of developing as a toner image.

  In the touch-down development method, toner is transferred from the toner layer of the developing roller to the photosensitive drum and developed, and then the toner layer remaining on the developing roller is scraped off by a magnetic brush formed of a developer on the surface of the magnetic roller. Collect the toner.

However, when toner collection is insufficient, a history is left, and image defects such as ghosts occur.
In particular, the toner layer is scraped off by a carrier. If the carrier has a small diameter, the magnetic force per carrier particle is small, so that the magnetic brush becomes soft or the carrier electrically moves to the developing roller. There is a tendency that a long magnetic brush cannot be formed due to the influence of so-called carrier pulling or the like, and the scraping power is reduced and the recoverability is deteriorated.

  In recent years, the toner has been required to have a smaller diameter for the purpose of improving the image quality, and accordingly, the carrier has to have a smaller diameter, and the above-described tendency has become stronger.

  Therefore, in order to solve this problem, Patent Document 2 proposes a method in which the developer filling density at a position where the developing roller and the magnetic roller face each other is set to a predetermined value or more to ensure the scraping force by the magnetic brush. is doing.

  However, in this method, when the carrier has a small diameter, the possibility of causing the carrier pulling is still high, and even with the same developer filling density, the amount of carrier is reduced, and the scraping power is reduced to obtain a sufficient effect. First, there are problems such as density difference (solid image unevenness) depending on the number of rotations of the developing roller when a solid image is printed, ghosting, and excessive developer, resulting in image failure due to developer leakage. There was a problem.

JP 2004-347707 A Japanese Patent Laid-Open No. 10-123841

  The problem to be solved by the present invention is that even if the carrier has a small diameter, the toner is collected from the toner layer on the developing roller, so that no solid image unevenness or ghost image occurs, and no developer leakage occurs for a long time. It is an object of the present invention to provide a developing device capable of obtaining a good image over a long period of time and an image forming apparatus to which the developing device is applied.

  According to a first aspect of the present invention, there is provided a photosensitive drum for forming an electrostatic latent image, a toner carrier that is rotatably supported facing the photosensitive drum, and holds toner on an outer peripheral portion thereof, and the toner carrier And a developer carrier that holds a two-component developer composed of a toner and a carrier, the toner carrier and the developer carrier, The present invention relates to a developing device having a gap of a predetermined distance, wherein the carrier volume abundance represented by the following formula is 16% or more and 24% or less.

CVP = {M × (100−TC) / 100} / ρ / D × 100
CVP: Carrier volume abundance ratio (%)
M: transport amount of two-component developer per unit area on developer carrier TC: toner concentration in developer (toner weight / carrier weight × 100)
ρ: True specific gravity of carrier D: Distance of gap between developer carrier and toner carrier

  According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein a gap distance between the toner carrier and the developer carrier is 0.2 mm or more and 0.5 mm or less.

  The invention according to claim 3 relates to the developing device according to claim 1 or 2, wherein a plurality of grooves extending in the longitudinal direction are formed in parallel on the surface of the developer carrying member. .

  A fourth aspect of the present invention relates to an image forming apparatus including the developing device according to any one of the first to third aspects.

  According to the first aspect of the present invention, a photosensitive drum that forms an electrostatic latent image, a toner carrier that is rotatably supported facing the photosensitive drum, and holds toner on an outer peripheral portion, and the toner A developer carrier that holds a two-component developer composed of toner and a carrier, is rotatably supported opposite to the carrier, and has a built-in magnetic member. The toner carrier and the developer carrier are predetermined. Since the gap of the distance is present and the carrier volume existence ratio is 16% or more in the gap, the toner can be collected from the toner layer on the toner carrier even if the carrier has a small diameter. Does not generate images. Further, since the developer leakage does not occur when the content is 24% or less, a good image can be obtained over a long period of time.

  According to the second aspect of the present invention, when the gap distance between the toner carrier and the developer carrier is 0.5 mm or less, the magnetic force of the developer carrier can be strongly received to prevent carrier pulling. In addition, since the distance between the toner carrier and the developer carrier is 0.2 mm or more, the developer leakage due to the developer carrier and the toner carrier being too close can be prevented, so that a good image can be obtained. .

  According to the third aspect of the present invention, a plurality of grooves extending in the longitudinal direction are formed in parallel on the surface of the developer carrying member, so that the number of printed sheets can be increased. When the speed is increased, even if the carrier has a small diameter, the developer does not slip on the surface of the developer carrying member, so that sufficient developer can be supplied and a good image can be obtained over a long period of time. .

  According to the fourth aspect of the present invention, by providing the developing device according to any one of the first to third aspects, it is favorable over a long period of time without causing solid image unevenness, ghost image, or developer leakage. An image can be obtained.

Hereinafter, preferred embodiments of a developing device and an image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic sectional view in side view of a developing device (1) according to the present invention.
As shown in FIG. 1, the developing device (1) according to the present invention includes a magnetic roller (11) in a housing (10), a developing roller (12) facing the magnetic roller (11), and a surface of the magnetic roller (11). A regulating blade (13) in contact with the stirring member (14) is provided. The magnetic roller (11) and the developing roller (12) have a gap (G) of a predetermined distance.
The photosensitive drum (2) is disposed outside the housing (10) so as to face the developing roller (12), and the developing roller (12) and the photosensitive drum (2) have a gap of a predetermined distance.
In this embodiment, the magnetic roller (11) is an embodiment of the developer carrier, and the developing roller (12) is an embodiment of the toner carrier.

The two-component developer containing toner and carrier is stirred and charged by the stirring member (14), and is transported and carried on the surface of the magnetic roller (11).
The two-component developer carried on the surface of the magnetic roller (11) forms a magnetic brush along the magnetic lines of force of the magnetic roller (11) and is regulated by the regulating blade (13), and then the magnetic roller (11) and the developing roller (12) is conveyed to the opposing gap (G), and a bias voltage is applied, whereby only the toner is transferred to the developing roller (12), and a thin toner layer is formed on the surface of the developing roller (12). The The toner carried on the surface of the developing roller (12) is biased to develop the electrostatic latent image formed on the photosensitive drum (2) to form a toner image.

After developing the photosensitive drum (2), the toner remaining on the developing roller (12) without being developed is scraped and collected by the magnetic brush.
FIG. 2 is a schematic diagram showing the behavior of the magnetic brush in the gap (G) where the magnetic roller (11) and the developing roller (12) face each other.

In FIG. 2, the upper part is a magnetic roller (11), the lower part is a developing roller (12), and the narrowest part forms a gap (G) having a distance (D).
Two-component developers are arranged along the magnetic field lines (E) of the magnetic roller (11) to form the magnetic brush (111).
The magnetic roller (11) and the developing roller (12) rotate in the counter direction (A and B directions in the drawing), respectively, and increase the scraping power of the undeveloped toner on the developing roller (12) by the magnetic brush (111). Yes.

  The magnetic brush (111) has its tip in contact with the developing roller (12) in the gap (G), a bias voltage is applied to transfer only the toner to the developing roller (12), and the thin toner layer (121) is formed. Then, the toner thin layer (121) remaining on the developing roller (12) without being developed from the developing roller (12) to the photosensitive drum (2) is scraped and collected.

Here, if the carrier particles have a small diameter, the magnetic force per carrier particle is weakened and the magnetic brush (111) becomes soft, or the magnetic force of the magnetic roller (11) reaches the tip of the magnetic brush (111). In some cases, the scraping force may be reduced due to so-called carrier pulling or the like in which the carrier is electrically moved to the developing roller (12).
In the present invention, in the gap (G), this is prevented by setting the carrier volume abundance represented by the following formula to 16% or more and 24% or less.

CVP = {M × (100−TC) / 100} / ρ / D × 100
CVP: Carrier volume abundance ratio (%)
M: transport amount of two-component developer per unit area on developer carrier TC: toner concentration in developer (toner weight / carrier weight × 100)
ρ: True specific gravity of carrier D: Distance of gap between developer carrier and toner carrier

That is, when the carrier volume abundance ratio is 16% or more, there is a sufficient amount of carriers, so that even if carrier pulling occurs, the scraping force of the magnetic brush (111) can be secured and the toner carrier can be secured. Since toner can be collected from the toner layer, solid image unevenness and ghost images are not generated.
Further, since the carrier volume abundance ratio is 24% or less, the developer does not become excessive in the gap (G), and the developer leakage does not occur and the image defect does not occur. A good image can be obtained.

  Moreover, it is preferable that the distance (D) of the narrowest part of a gap (G) is 0.2 mm or more and 0.5 mm or less.

  The further away from the magnetic roller (11), the less the carrier is restrained by the magnetic force of the magnetic roller (11) and the carrier is likely to be pulled. However, the distance (D) is 0.5 mm or less. This is because it is difficult for carrier pulling to occur, and because the distance (D) is 0.2 mm or more, the gap (G) is wide and it is difficult for the developer to be excessive.

  FIG. 3 is a schematic plan view showing the surface of the magnetic roller (11) in which both end portions such as bearings are omitted, and FIG. 4 is a view taken along the line CC in FIG. ), The internal structure and the like are omitted.

As shown in FIGS. 3 and 4, it is preferable that a plurality of grooves (112) extending in the longitudinal direction are formed in parallel on the surface of the magnetic roller (11) except for both end portions thereof.
In order to cope with the increase in the number of printed sheets, even when the speed of the magnetic roller (11) is increased in association with the speed of the photosensitive drum (2) and the developing roller (12), even if the carrier has a small diameter. This is because sufficient developer can be supplied without causing the developer to slip on the surface of the magnetic roller (11).

  The number of grooves (112) is eight in FIG. 4, but is not particularly limited. Further, the width and depth of the groove (112) are not particularly limited.

The developing device in the present invention can be suitably used for an image forming apparatus.
A photosensitive member; a charging unit that charges the photosensitive member; an exposure unit that exposes and forms an electrostatic latent image on a predetermined region on the photosensitive member; a developing unit that develops the electrostatic latent image on the photosensitive member; and a photosensitive member In an image forming apparatus including a transfer unit for transferring the developer image on the recording medium, a solid image unevenness, a ghost image, or a developer leakage is generated by employing the developing device according to the present invention as the developing unit. And good images can be obtained over a long period of time.

  Hereinafter, the present invention will be described clearly by showing examples, but the present invention is not limited to these examples.

The test body 1 has a carrier having a particle size of 30 μm, a resistance value of 5.0 × 10 ¹⁰ Ωcm, and a saturation magnetization of 30 emu / g, and the toner concentration in the developer (toner weight / carrier weight × 100) is 12%. Some developer is used.
The test body 2 has a carrier having a particle size of 30 μm, a resistance value of 5.0 × 10 ¹⁰ Ωcm, and a saturation magnetization of 40 emu / g, and the toner concentration in the developer (toner weight / carrier weight × 100) is 12%. Some developer is used.
The test body 3 has a carrier having a particle diameter of 35 μm, a resistance value of 1.0 × 10 ¹² Ωcm, and a saturation magnetization of 30 emu / g, and the toner concentration in the developer (toner weight / carrier weight × 100) is 12%. Some developer is used.
The test body 4 has a carrier having a particle diameter of 45 μm, a resistance value of 1.0 × 10 ¹³ Ωcm, and a saturation magnetization of 50 emu / g, and the toner concentration in the developer (toner weight / carrier weight × 100) is 12%. Some developer is used.

  (Example 1) For specimen 1, assuming that the carrier volume abundance (CVP) in gap (G) is 18.4% and distance (D) is 0.35 mm, (I) the amount of magnetic brush is calculated, (II ) When there is a solid image printed, the presence or absence of a density difference between the first and second rounds of the developing roller (12), (III) the presence or absence of developer leakage, and (IV) the presence or absence of carrier adhesion in the printed image are confirmed. .

  (Example 2) For the test body 2, the carrier volume abundance ratio (CVP) in the gap (G) is set to 16.0%, the distance (D) is set to 0.50 mm, and (I) to (IV) are confirmed.

  (Example 3) With respect to the specimen 3, (I) to (IV) are confirmed by setting the carrier volume abundance (CVP) in the gap (G) to 24.0% and the distance (D) to 0.30 mm.

  (Example 4) With respect to the test body 4, the carrier volume existence ratio (CVP) in the gap (G) is 21.5%, the distance (D) is 0.20 mm, and (I) to (IV) are confirmed.

  (Example 5) For the test body 4, the carrier volume abundance ratio (CVP) in the gap (G) is set to 16.7%, the distance (D) is set to 0.55 mm, and (I) to (IV) are confirmed.

  (Comparative example 1) About the test body 1, (I)-(IV) is confirmed by making carrier volume presence rate (CVP) in gap (G) 24.6% and distance (D) 0.35 mm.

  (Comparative example 2) About the test body 2, (I)-(IV) is confirmed for carrier volume existence rate (CVP) in a gap (G) as 15.6% and distance (D) as 0.35 mm.

  The results are shown in Table 1. In Table 1, with regard to the presence or absence of (II) to (IV), the case of “None” is “O”, the case of “Yes” is “X”, and “Yes”, but there is no problem in practical use. "Is" ".

  According to the results of Comparative Examples 1 and 2 shown in Table 1, when the carrier volume existence ratio in the gap (G) is 16% or less, (II) 1 of the developing roller (12) when the solid image is printed If the density difference between the second and second rounds occurs and exceeds 24%, (III) developer leakage occurs and a good image cannot be obtained.

  On the other hand, according to the results of Examples 1 to 5 shown in Table 1, when the carrier volume existence ratio in the gap (G) is 16% or more and 24% or less, (II) the developing roller when the solid image is printed It can be said that a good image can be obtained without the density difference between the first and second rounds of (12) and (III) developer leakage.

  Further, according to the result of Example 5, when the distance (D) exceeds 0.5 mm, although there is no problem in actual use, (IV) carrier adhesion in the printed image is confirmed, causing carrier pulling. I understand that.

  According to the results of Examples 1 to 4, when the distance (D) is 0.2 mm or more and 0.5 mm or less, (IV) carrier adhesion in the printed image is not confirmed, and carrier pulling does not occur. It can be said that the distance (D) of the gap (G) is preferably 0.2 mm or more and 0.5 mm or less.

  The present invention is suitably used for a developing device adopting a touch-down developing method as a developing method and an image forming apparatus such as a copying machine, a printer, and a facsimile employing the developing device.

FIG. 3 is a schematic sectional view in side view of the developing device according to the present invention. It is a schematic diagram which shows the behavior of the magnetic brush of the developing device according to the present invention. It is a schematic plan view showing the surface of the magnetic roller of the developing device according to the present invention. It is a schematic diagram explaining the surface shape of the magnetic roller of the developing device according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing device 11 Magnetic roller 111 Magnetic brush 112 Groove 12 Developing roller 121 Toner layer 2 Photosensitive drum

Claims (4)

A photosensitive drum for forming an electrostatic latent image;
A toner carrier that is rotatably supported facing the photosensitive drum and holds toner on the outer periphery; and
A developer carrying member that is rotatably supported facing the toner carrying member, has a built-in magnetic member, and holds a two-component developer composed of toner and a carrier,
The toner carrier and the developer carrier have a gap of a predetermined distance, and the carrier volume abundance expressed by the following formula is 16% or more and 24% or less in the gap. Development device.
CVP = {M × (100−TC) / 100} / ρ / D × 100
CVP: Carrier volume abundance ratio (%)
M: transport amount of two-component developer per unit area on developer carrier TC: toner concentration in developer (toner weight / carrier weight × 100)
ρ: True specific gravity of carrier D: Distance of gap between developer carrier and toner carrier   2. The developing device according to claim 1, wherein a gap distance between the toner carrier and the developer carrier is 0.2 mm or more and 0.5 mm or less.   The developing device according to claim 1, wherein a plurality of grooves extending in the longitudinal direction are formed in parallel on the surface of the developer carrying member.   An image forming apparatus comprising the developing device according to claim 1.

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