JP2002229327A - Developing roll and developing device provided therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing roll by which the inclination of developing γis made to be steep even when the surface of the roll is worn with the lapse of time and also toner is saturated at developing potential being low potential of <=150 V and whose durability is improved, and a developing device provided therewith. SOLUTION: This developing roll 10 is successively provided with a core shaft 1, an elastic layer 2 and a surface layer 3, and its volume resistance at an initial stage is set to <=1.5×104 Ωcm, its capacitance at the initial stage is set to >=1.5×10-4 F/m2, and besides, the volume resistance after the 75% of the surface layer 3 is worn is set to <=1.5×106 Ωcm, and also the capacitance after the 75% of the surface layer 3 is worn is set to >=1.0×10-6 F/m2. The JIS-A hardness of the roll 10 is desirably 25 to 50. The thickness of the surface layer of the roll 10 is desirably <=30 μm, and the ASKER-C hardness of the roll 10 including the surface layer is desirably <=55 (303 g load).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing roll used in an electrophotographic apparatus such as a copying machine, a printer, a facsimile or an electrostatic recording apparatus.

[0002]

2. Description of the Related Art Conventionally, in the field of electrophotographic apparatuses such as copiers, printers and facsimile machines, especially in the field of small electrophotographic apparatuses, simplification of maintenance has been promoted. As described in the official gazette (hereinafter referred to as "prior art 1"), an electrostatic latent image formed on an image carrier such as a photosensitive member surface, photosensitive paper, or recording paper is formed using a one-component toner. A developing device of a type which develops by using a developing device has been put to practical use. FIG. 11 is a schematic explanatory view of such a conventional developing device.

As shown in FIG. 11, a photosensitive drum 101 includes a surface portion A and a base portion B. The surface layer portion A functions as an image carrier, and the base portion B functions as an image carrier support member. The base portion B adheres a relatively elastic conductive rubber 103 to the surface of the metal drum 102, and
A flexible metal foil 104 such as an aluminum foil is adhered thereon, and the surface layer portion A further comprises a photoconductive insulator layer 1 formed by evaporating a metal such as selenium thereon.
It consists of 05. On the surface of the photosensitive drum 101, a developing roll 106 is provided in pressure contact. Development roll 10
6 is a metal roll 107 and an elastic layer 10 made of conductive synthetic rubber, urethane foam or the like formed on its surface.
Eight. Such a plasticizer or a low-molecular substance bleeding out from the elastic layer 108 of the developing roll 106 contaminates the surface portion A of the photosensitive drum 101,
Since toner adhesion (tacking) and filming occur on the elastic layer 108 of the developing roll 106, the developing roll 1
In addition, the surface of the elastic layer 108 is coated with a surface layer (not shown) made of a resin having good toner release properties to prevent bleed-out of the plasticizer and the low-molecular substance and to prevent adhesion and filming of the toner. Some development rolls have been prevented.

[0004] A bias power supply 109 is connected between the developing roll 106 and the base portion B of the photosensitive drum 101. A hopper 111 containing a one-component non-magnetic toner 110 is provided at an upper portion of the developing roll 106 with a lower portion of the opening at a predetermined interval on the surface of the developing roll 106. Inside the right side wall of the hopper 111,
The friction charging member 112 is adhered. Development roll 10
On the right side of 6, a leveling member 113 is provided with its surface pressed against the surface of the developing roll 106. The leveling member 113 has a rubber layer 11 on the surface of the metal roll 114.
5 is adhered, and a triboelectric charging member 116 is coated thereon, and is provided so as not to rotate.

According to the developing roll 106, a thin layer of toner is carried on the surface thereof and is brought into contact with the photosensitive drum 101 on which an electrostatic latent image is formed. The electrostatic latent image formed on the photosensitive drum 101 is visualized. In such a developing roll 106, it is necessary to control the polarity and amount of charging of the toner by frictional charging due to contact between the toner and the surface of the developing roll 106. The movement of the toner to the photosensitive drum 101 is performed by selecting an image portion and a non-image portion (background portion) of the electrostatic latent image according to the polarity of the toner charge and the development electrolysis. According to this apparatus, there is an advantage that colorization is easy without using a magnetic material for the toner.

Japanese Patent Publication No. Sho 64-1022 (hereinafter referred to as "prior art 2") discloses a developing device in which one-component non-magnetic toner particles are transferred from a magnetic brush to a developing roller. I have. FIG. 12 is a schematic explanatory view of such a conventional developing device.

As shown in FIG. 12, a rotatable magnetic roller 208 which forms a magnetic brush 212 by adsorbing a magnetic carrier for charging one-component non-magnetic toner particles.
And a magnetic brush 2 formed between the magnetic roller 208 and the electrostatic image holding member 201 and formed by the magnetic roller 208.
And a developing roller 211 for carrying the charged toner 207 separated from the developing roller 12 and developing the electrostatic image on the electrostatic image holding member 201. A developing device 203 that forms an electric field and transfers the one-component non-magnetic toner 207 from the magnetic brush 212 to the developing roller 211 is described. According to the developing device 203, the toner charge is started up with the two-component developer, and the toner 207 is supplied onto the developing roller 211 by the magnetic brush 212 formed on the magnetic roller 208. By eliminating the members and reducing the stress on the toner particles 207, the developing device 203 can be kept stationary.

[0008]

In a conventional developing device of the type described in "Prior Art 1", which develops an electrostatic latent image formed on an image carrier using a one-component toner, Adhesion of toner to the toner thin layer blade, toner filming to the developing roll, generation of scratches on the surface of the developing roll over time, toner charge amount due to toner deterioration (stress), and Due to various problems such as a change in the amount of toner attached over time and background contamination when replenishing toner,
There is no choice but to take a cartridge form that can be replaced after printing several tens of k levels, and therefore, there is a problem that the developing device cannot be installed.

In order to solve such a problem, "Prior art 2" has been proposed. However, "Prior art 2" shortens the life of the photosensitive drum because the photosensitive drum is charged to a high charging potential. Attempts have been made to charge the photosensitive drum to a low charging potential to reduce deterioration during charging. As described above, when the photosensitive drum is charged to a low charging potential, the developing bias needs to be set low. Further, from the viewpoint of high image quality, from multi-valued (the image writing modulation pattern is output using a large number of gradations) to binary (the image writing modulation pattern is output using the two gradations, ie, In order to make the dot density the same and to change the tone depending on how the dots are hit, the development γ (gradient of the characteristic curve of the image density with respect to the electrostatic potential) is made as high as possible, and the saturation development is performed. The need has arisen to minimize the potential as much as possible.

An object of the present invention is to solve such a problem. That is, according to the present invention, even when abrasion occurs on the roll surface over time, the inclination of the development γ can be made steep and the
It is an object of the present invention to provide a developing roller with improved durability that can saturate toner with a developing potential of a low potential of V or less, and a developing device having the same.

[0011]

Means for Solving the Problems The present inventor has proposed that, in a developing roll having a core axis, an elastic layer and a surface layer in order, the initial volume resistance is not more than 1.5 × 10 ⁴ Ω · cm, The initial capacitance is 1.5 × 10 ⁻⁴ / m ² or more, and the volume resistance after 75% of the surface layer is worn is 1.5 × 10 ⁶ Ω · cm or less. The capacitance after the 75% of the surface layer is worn is 1.0 × 10 ^−6.
/ m ² or more, the slope of development γ can be steep even if the roll surface is worn over time,
It is possible to provide a developing roller having an improved durability capable of saturating toner with the following low-potential developing potential (that is, a difference between the surface potential of an image area on a photoconductor and a developing bias) and a developing device having the same. To complete the present invention.

That is, according to the first aspect of the present invention, in a developing roll having a core axis, an elastic layer, and a surface layer in order, the initial volume resistance is set to 1.5 × 10 ⁴ Ω · cm or less, The initial capacitance is 1.5 × 10 ⁻⁴ F
/ m ² or more, and the volume resistance after 75% of the surface layer is worn is 1.5 × 10 ⁶ Ω · cm or less, and the capacitance after 75% of the surface layer is worn. 1.
A developing roll characterized by having a pressure of 0 × 10 ⁻⁶ F / m ² or more.

According to a second aspect of the present invention, in the first aspect of the invention, the JIS-A hardness is 25 to 50.
Degree.

According to a third aspect of the present invention, in the first aspect, the surface layer has a thickness of 30 μm.
m or less and the AS of the developing roll including the surface layer
KER-C hardness is 55 degrees (303 g load) or less.

The invention described in claim 4 is the first invention.
3. The developing roller according to any one of 3) is provided in parallel contact with the photosensitive drum, a toner supply roll is provided to face the development roll, and a doctor blade is provided on the supply roll to provide a carrier and a toner. And a magnetic brush in which the toner is mixed is brought into contact with the developing roll to supply only the toner onto the developing roll.

According to a fifth aspect of the present invention, in the invention of the fourth aspect, when the difference between the surface potential of the image area of the photosensitive member and the developing bias is 150 V or less, the amount of toner adhering to the photosensitive member is reduced. It is characterized by being saturated.

[0017]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a developing roll showing one embodiment of the present invention, FIG. 2 is a schematic explanatory diagram of a developing device using the developing roll showing one embodiment of the present invention, and FIG. 3 is an explanatory diagram for explaining a method of measuring the volume resistance and the capacitance of the developing roll.

In FIG. 1, reference numeral 10 denotes a developing roll.
The developing roll 10 has a core shaft 1, an elastic layer 2, and a surface layer 3 in this order. The developing roll 10 has an initial volume resistance of 1.5 × 10 ⁴ Ω · cm or less and an initial capacitance of 1.5 × 10 ⁻⁴ F / m ² or more.
The volume resistance after 75% of the surface layer is worn is 1.5 ×
10 ⁶ Ω · cm or less and 75% of the surface layer
The capacitance after wear is set to 1.0 × 10 ⁻⁶ F / m ² or more.

The developing roll 10 of the present invention is used in a process (binary developing process) for developing in a region where the development γ (gradient of the characteristic curve of the image density with respect to the electrostatic potential) is saturated. In order to reduce the damage of
The initial volume resistance is 1.5 × 10 ⁴ Ω · cm or less, and the initial capacitance is 1.5 × 10 ⁻⁴ F / m ^2.
As described above, development γ can be saturated with a low development potential. The electric resistance and the capacitance may change when the roll surface wears over time, causing a problem that the development γ is not saturated. However, the development roll 10 of the present invention has The volume resistance after 75% wear is reduced to 1.5 × 10 ⁶ Ω · cm or less, and the capacitance after 75% of the surface layer is worn is reduced to 1.0 × 10 ^−6. Since the electrostatic capacity is as high as F / m ² or more, there is no problem that the development γ is not saturated. Conventionally, the concept of the durability of the developing roll is to increase the abrasion resistance of the surface and to reduce the coefficient of friction. However, according to the developing roll 10 of the present invention, the surface layer is worn. Based on the idea, the electrical characteristics capable of saturating the amount of the developing toner at a low developing potential of 150 V, that is, the volume resistance and the capacitance at the initial stage and after the 75% of the surface layer is worn are defined. Improved durability.

Therefore, according to the developing roll 10 of the present invention, the initial volume resistance is 1.5 × 10 ⁴ Ω · cm or less, and the initial capacitance is 1.5 × 10 ^-4. F
/ m ² or more, and the volume resistance after 75% of the surface layer is worn is 1.5 × 10 ⁶ Ω · cm or less, and the capacitance after 75% of the surface layer is worn. 1.
By setting it to 0 × 10 ⁻⁶ F / m ² or more, the slope of the development γ can be made steep even if the roll surface is worn over time, and the development potential at a low potential of 150 V or less (that is, the image on the photoreceptor). (The difference between the surface potential of the portion and the developing bias), the toner can be saturated.
Durability can be improved.

Important characteristics of the developing roll 10 of the present invention are as follows.
In terms of its electric characteristics, the electric resistance and the capacitance are set to the low electric resistance and the high capacitance, respectively, as described above. In recent years, as the life of the system has been prolonged (especially the photoreceptor), attempts have been made to reduce the deterioration of the photoreceptor by lowering the charging potential, and accordingly the developing bias must be set lower. Further, in order to change from multiple values to binary values, high development γ is required. Since conductivity is required, it is necessary to add a conductive agent such as carbon black or metal oxide.

The developing roll 10 has an elastic layer 2 made of rubber or elastomer around a core shaft 1 made of metal. As the elastic layer 2, for example, a rubber or an elastomer such as ethylene propylene rubber, butadiene rubber, nitrile rubber, styrene rubber, isoprene rubber, silicone rubber, urethane rubber, or urethane foam can be used. As for the hardness, in order to improve the dot reproducibility of the image, it is better that the nip width is not too wide, and the hardness is preferably 25 to 50 JIS-A hardness.

On the outer peripheral surface of the elastic layer 2, for example, a surface layer formed of a resin composition obtained by adding a conductive agent to a solvent-soluble fluororesin which is a copolymer of a fluoroolefin and an ethylenically unsaturated monomer. Three. The resin composition described here is merely an example, and other resin compositions may be used as long as the object of the present invention is not contravened. The surface layer 3 can be formed, for example, by coating a known coating such as a dip method, a spray coat, a roll coat or the like, or a tube-shaped molded product. The thickness of the surface layer 3 is preferably 30
μm or less. When the thickness of the surface layer 3 exceeds 30 μm, it becomes harder than the hardness of the elastic layer, and it is easily broken.

JIS of developing roll 10 including surface layer 3
-A hardness is preferably 25 to 50 degrees. JIS
If the -A hardness is less than 25 degrees, the nip width with the photoreceptor becomes too wide, and the toner in the developed image (dot) portion is disturbed. Due to too high a pressure, the toner cannot sufficiently adhere to the image on the photoconductor. The ASKER-C hardness of the developing roll 10 including the surface layer 3 is preferably 55 degrees or less under a load of 303 g. Since the surface layer 3 needs to be hardened to some extent in order to improve dot reproducibility, its ASKER-C hardness is preferably 5
5 degrees or less. In JIS-A hardness measurement, ASKER-
There is no difference as in C hardness.

As shown in FIG. 2, the developing device 20 of the present invention
According to the above, the toner is charged by the two-component developer 16 in which the carrier and the toner are mixed. Developing device 2
At 0, the developing roll 10 is provided in parallel contact with the photosensitive drum 11, a toner supply roll 14 is provided facing the development roll 10, and a doctor blade 15 is provided on the supply roll 14. By bringing the magnetic brush, in which the carrier and the toner are mixed, into contact with the developing roll 10, only the toner is supplied onto the developing roll 10. Then, in the developing device 20, the two-component developer 16 is conveyed to a supply roll 14 composed of a magnetic roll, and the two-component developer 16 is thinned by a doctor blade 15 provided on the toner supply roll 14. Thus, a magnetic brush in which the carrier and the toner are mixed is formed. When the magnetic brush thus formed is brought into contact with the developing roll 10 at the thin toner layer forming section 13, only the toner is supplied onto the developing roll 10. 17 is
This is a toner supply unit.

The toner supplied on the developing roll 10 is
An electrostatic latent image portion of the photosensitive drum 11 by the developing roll 10;
That is, the latent image is transported to the developing unit 12 (one-component contact development) to develop the latent image. The toner supply roll 14 and the developing roll 10 can be used in non-contact, and the developing roll and the photoconductor can be used in either contact or non-contact. However, contact development is desirable from the viewpoint of image quality. Although not shown, between the toner supply roll 14 and the development roll 10, the development roll 10 and the photosensitive drum 1
1, a bias voltage is applied across the power supply. The bias to the developing roll 10 includes DC, DC + AC, etc., but DC bias is desirable from the viewpoint of cost. In this embodiment, a drum photoreceptor is used as the photoreceptor substrate, but a belt photoreceptor can also be used. By using such a developing device 20, the number of members that come into contact with the developing roll 10 is reduced, so that filming on the developing roll 10 can be prevented. In addition, the problem of toner sticking to the blade, which has been a problem in the conventional blade toner thin layer type developing device, is eliminated.

The developing device 20 of the present invention saturates the amount of toner adhering to the photoconductor when the difference between the surface potential of the image area (not shown) of the photoconductor and the developing bias is 150 V or less. .

[0028]

(Example 1) A resin composition comprising a polyol (manufactured by Sumitomo Bayer Urethane Co., Ltd.) in which 5% by weight of carbon black is dispersed and an isocyanate (Coronate T65) is coated with an adhesive in advance of stainless steel having a diameter of 8 mm. (SUS) A urethane elastomer layer was formed by coating around the core axis by a one-shot method, and the urethane elastomer layer was ground to an outer diameter of 16 mm to adjust the diameter of the urethane elastomer layer to 16 mm. A roll having a thick elastic layer was formed. Then, fluororesin (THV220P, manufactured by Sumitomo 3M) is converted to methyl ethyl ketone (MEK).
Then, 20% by weight of carbon black (based on the fluororesin) is dispersed in the fluororesin solution to obtain a fluororesin coating solution, and the fluororesin coating solution is spray-coated on the elastic layer of the roll. The developing roll was obtained by evaporating the solvent in an oven to form a surface layer having a thickness of 20 μm.

Example 2 In the same manner as in Example 1, a roll having an elastic layer on the surface of a SUS core shaft was formed. And M
A conductive urethane paint (suprex, manufactured by Nippon Milactran Co., Ltd.) using EK as a solvent is spray-coated on the elastic layer of the roll, and then the solvent is volatilized in an oven to a thickness of 2%.
A developing roll was obtained by forming a surface layer of 0 μm.

Example 3 In the same manner as in Example 1, a roll having an elastic layer on the surface of the SUS core shaft was formed. After diluting a fluororesin (Lumiflon, manufactured by Asahi Glass Co., Ltd.) composed of a copolymer of a fluoroolefin and an ethylenically unsaturated monomer with a mixed solvent of toluene and xylene, a metal oxide is added to the fluororesin solution. (ITO) 66% by weight (relative to the fluororesin) and 20% by weight (relative to the fluororesin) of the curing agent are dispersed to form a fluororesin coating liquid, and this fluororesin coating liquid is sprayed on the elastic layer of the roll. After coating, the solvent was volatilized in an oven, and then the fluororesin was cured by heating to form a surface layer having a thickness of 20 μm, thereby forming a developing roll.

Comparative Example 1 In the same manner as in Example 1, a roll having an elastic layer on the surface of a SUS core shaft was formed. Then, after dissolving a fluororesin (THV220P, manufactured by Sumitomo 3M) in MEK, 3% by weight of carbon black (based on the fluororesin) is dispersed in the fluororesin solution to form a fluororesin coating liquid. The coating liquid was spray-coated on the elastic layer of the roll, and then the solvent was volatilized in an oven to form a surface layer having a thickness of 20 μm.

Comparative Example 2 In the same manner as in Example 1, a roll having an elastic layer on the surface of the SUS core shaft was formed. After diluting a fluororesin (Lumiflon, manufactured by Asahi Glass Co., Ltd.) composed of a copolymer of a fluoroolefin and an ethylenically unsaturated monomer with a mixed solvent of toluene and xylene, a metal oxide is added to the fluororesin solution. (ITO) 58% by weight (relative to the fluororesin) and 20% by weight (relative to the fluororesin) of the curing agent are dispersed to form a fluororesin coating liquid, and this fluororesin coating liquid is sprayed on the elastic layer of the roll. After coating, the solvent was volatilized in an oven, and then the fluororesin was cured by heating to form a surface layer having a thickness of 20 μm, thereby forming a developing roll.

(Comparative Example 3) A rubber composition obtained by adding additives such as calcium carbonate, sulfur and a vulcanization accelerator to epichlorohydrin rubber (manufactured by Daiso Co., Ltd.) was prepared by applying an adhesive in advance and having a diameter of 8 mm. The circumference of a stainless steel (SUS) core shaft is coated by press molding to form a urethane elastomer layer, and the epichlorohydrin rubber layer is ground to an outer diameter of 16 mm to adjust the diameter of the SUS shaft to 16 mm. A roll having a 4 mm-thick elastic layer on the surface was formed. Then, a fluororesin (manufactured by Sumitomo 3M, THV220)
P) is dissolved in methyl ethyl ketone (MEK),
20% by weight of carbon black (based on the fluororesin) is dispersed in the fluororesin solution to form a fluororesin coating solution. The fluororesin coating solution is spray-coated on the elastic layer of the roll, and then the solvent is volatilized in an oven. Then, a surface layer having a thickness of 20 μm was formed to obtain a developing roll.

Comparative Example 4 A resin composition comprising a polyol (manufactured by Sumitomo Bayer Urethane Co., Ltd.) in which 1% by weight of carbon black was dispersed and an isocyanate (Coronate T65) was coated with an adhesive in advance of stainless steel (diameter 8 mm). SUS) A urethane elastomer layer is formed by coating around the core axis by a one-shot method, and the outer diameter of the urethane elastomer layer is adjusted to a diameter of 16 mm. A roll having an elastic layer was formed. And the fluororesin (Sumitomo 3M
Manufactured by THV220P) with methyl ethyl ketone (ME
K), 20% by weight of carbon black (based on the fluororesin) is dispersed in the fluororesin solution to obtain a fluororesin coating solution, and the fluororesin coating solution is spray-coated on the elastic layer of the roll. After that, the solvent was volatilized in an oven to form a surface layer having a thickness of 20 μm, thereby forming a developing roll.

In evaluating the developing rolls obtained in Examples 1 to 3 and Comparative Examples 1 to 4, these developing rolls were forcibly abraded by tape polishing. The polishing conditions were as follows: work rotation speed: 1540 rpm, rough tape: # 1000, tape tension: 3 kgf / cm ²
And the operation was terminated when 75% of the initial surface layer film layer was worn. The “75%” is approximately equal to the developing roll linear velocity of 198 mm / sec (0.254 sec / rotation).
The amount of wear on the surface when the developing roll rotating in c) rotates 2832000 turns is equal to, and the linear velocity of the photoreceptor is
In the case of sec, this corresponds to 400 k sheets (the number of prints).

Then, the relationship between the initial development potential (V) of the developing rolls obtained in Examples 1 to 3 and the amount of toner adhered on the photoreceptor (mg / cm ² ) was examined. 4 to 6 are graphs showing the relationship between the development potential (V) and the amount of toner adhered on the photoconductor (mg / cm ² ) in the initial stage of the development rolls obtained in Examples 1 to 3. Also,
The relationship between the developing potential (V) of the developing rolls obtained in Comparative Examples 1 and 2 at the initial stage and after abrasion and the amount of toner adhered on the photoreceptor (mg / cm ² ) was examined. FIGS. 7 to 10 are graphs showing the relationship between the developing potential (V) of the developing rolls obtained in Comparative Examples 1 and 2 at the initial stage and after abrasion, and the toner adhesion amount (mg / cm ² ) on the photoconductor. is there.

The “volume resistance (Ω · cm)”, “capacitance (F / cm ² )” and “volume resistance” of the developing rolls obtained in Examples 1 to 3 and Comparative Examples 1 to 4 at the initial stage and after the abrasion are obtained. "J
IS-A hardness (degree) "and" ASKER-C hardness (degree) "were measured, respectively, and" saturated development potential (development potential at which the amount of adhered toner on the photoreceptor is saturated) (V) "at the initial stage and over time. Was measured, and "dot reproducibility" was further evaluated. However, as for the “volume resistance (Ω · cm)”, as shown in FIG. 3, a roll is pressed in parallel to a parallel electrode, and 5 mm is applied to both shafts.
The measurement was performed by applying a voltage of 5 V between the conductive shaft and the parallel electrode while a load of 00 g was applied in the direction of the parallel electrode.
As for the “capacitance (F / m ² )”, as shown in FIG. 3, a roll is pressed in parallel to a parallel electrode, and a load of 500 g is applied to both shafts in the parallel electrode direction. A 1 V voltage was applied between the shaft and the parallel electrode for 30 seconds for measurement. The "dot reproducibility" was evaluated as "O" for superior and "X" for inferior. The results of these measurements are shown in Table 1 below.

[0038]

[Table 1]

The following can be understood from FIGS. 4 to 10 and Table 1. That is, in the first to third embodiments, since the “volume resistance (Ω · cm)” is low and the “capacitance (F / m ² )” is large at the initial stage and after abrasion, the developing γ is changed to a developing potential of 150 V. It can be saturated at the following low potentials, and has excellent dot reproducibility. In Comparative Example 1, the development γ was not saturated at 150 V or less at the initial stage and after abrasion. In Comparative Example 2, the development γ was initially 1
It is saturated at 50 V or less.
It is saturated below 0V. Neither of Comparative Examples 1 and 2 satisfy the required conditions for electrical characteristics. In Comparative Examples 3 and 4,
Although the development γ is saturated at 150 V or less, this is a level at which dot reproducibility becomes a problem. This may be due to the effect of roll hardness.

[0040]

(1) According to the invention described in claim 1
If the initial volume resistance is 1.5 × 10 ^Four Ω · cm or less
And the initial capacitance is 1.5 × 10^-FourF
/ m^TwoAbove, and 75% of the surface layer was worn
1.5 × 10⁶ Ω · cm or less
In addition, the capacitance after 75% of the surface layer is worn is 1.
0x10^-6F / m^TwoBy doing the above,
Steep slope of development γ even if wear occurs on the tool surface
With a low developing potential of 150 V or less (immediately
That is, the surface potential of the image area of the photoconductor and the developing bias
The difference) can saturate the toner, so that
Durability can be improved.

(2) According to the invention described in claim 2,
Since the JIS-A hardness is 25 to 50 degrees, dot reproducibility can be improved.

(3) According to the third aspect of the present invention,
The thickness of the surface layer is 30 μm or less, and the ASKER-C hardness of the developing roll including the surface layer is 55 degrees (303 degrees).
g load) or less, so that cracking of the surface layer and the like can be prevented, and dot reproducibility can be improved.

(4) According to the invention described in claim 4,
A developing roll is provided in parallel contact with the photosensitive drum, a toner supply roll is provided opposite the developing roll, and
A doctor blade is provided on the supply roll, and a magnetic brush in which carrier and toner are mixed is brought into contact with the development roll so that only the toner is supplied onto the development roll. And
It is possible to provide a developing device capable of obtaining high image quality, and (b) since the toner charge distribution on the developing roll becomes sharper compared to the toner charging in the developer, it is possible to reduce background contamination. it can.

(5) According to the invention described in claim 4,
When the difference between the surface potential of the image area of the photoconductor and the developing bias is 150 V or less, the amount of toner adhering to the photoconductor is saturated.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a developing roll according to an embodiment of the present invention.

FIG. 2 is a schematic explanatory view of a developing device using a developing roll according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram for explaining a method of measuring a volume resistance and a capacitance of a developing roll.

FIG. 4 shows a developing potential (V) and a toner adhesion amount (m) on a photoreceptor in the initial stage of the developing roll obtained in Example 1.
g / cm ² ).

FIG. 5 shows a developing potential (V) and a toner adhesion amount (m) on a photoreceptor in the initial stage of the developing roll obtained in Example 2.
g / cm ² ).

FIG. 6 shows a developing potential (V) and a toner adhesion amount (m) on a photoreceptor in the initial stage of the developing roll obtained in Example 3.
g / cm ² ).

FIG. 7 is a graph showing a relationship between an initial development potential (V) of a development roll and an amount of toner adhering on a photoreceptor (mg / cm ² ) obtained in Comparative Example 1.

FIG. 8 is a graph showing the relationship between the developing potential (V) and the amount of toner adhered on a photoreceptor (mg / cm ² ) in the initial stage of the developing roll after abrasion obtained in Comparative Example 1.

FIG. 9 is a graph showing the relationship between the initial development potential (V) of the developing roll and the amount of toner adhered on the photoconductor (mg / cm ² ) obtained in Comparative Example 2.

FIG. 10 is a graph showing the relationship between the developing potential (V) and the amount of toner adhered on a photoreceptor (mg / cm ² ) in the initial stage of the developing roll after abrasion obtained in Comparative Example 2.

FIG. 11 is a schematic explanatory view of a conventional developing device.

FIG. 12 is a schematic explanatory view of another conventional developing device.

[Explanation of symbols]

 Reference Signs List 1 core shaft 2 elastic layer 3 surface layer 10 developing roll 11 photoreceptor drum 12 developing unit (one-component contact development) 13 toner thin layer forming unit 14 toner supply roll 15 doctor blade 16 two-component developer 17 toner replenishing unit 20 developing device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H031 AC03 AC07 BA05 BA09 CA01 2H073 BA02 BA13 BA23 CA02 2H077 AC04 AC13 AD06 AD18 AD35 EA15 FA12 FA19 FA22 FA25 3J103 AA02 AA13 FA12 GA57 GA58 GA60 HA04 HA20 HA43 HA52 HA53 HA53

Claims (5)

[Claims] 1. A developing roll having a core axis, an elastic layer and a surface layer in order, has an initial volume resistance of 1.5 × 10
⁴ Ω · cm or less, the initial capacitance is 1.5 × 10 ⁻⁴ F / m ² or more, and the volume resistance after 75% of the surface layer is worn out is 1.5 × 10 ⁴ F / m ^2. 10 ⁶ Ω · c
m, and the electrostatic capacity after 75% of the surface layer is worn out is 1.0 × 10 ⁻⁶ F / m ² or more. 2. The developing roll according to claim 1, wherein the JIS-A hardness is 25 to 50 degrees. 3. The developing roll according to claim 1, wherein the thickness of the surface layer is 30 μm or less, and the ASKER-C hardness of the developing roll including the surface layer is 55 degrees (303 g load) or less. The developing roll of the above. 4. The developing roll according to claim 1, which is provided in parallel contact with the photosensitive drum, a toner supply roll is provided opposite to the development roll, and a toner supply roll is provided on the supply roll. A developing device provided with a doctor blade, wherein only a toner is supplied onto a developing roll by bringing a magnetic brush in which a carrier and a toner are mixed into contact with the developing roll. 5. The developing device according to claim 4, wherein the amount of toner adhering to the photoconductor is saturated when the difference between the surface potential of the image area of the photoconductor and the developing bias is 150 V or less.