JPH08179620A - Developing roller - Google Patents

Abstract

PURPOSE: To maintain a specified toner transporting rate or toner electrostatic charge quantity and to stably obtain high-grade images by specifying the nuclear depth roughness (Rk) stipulated in DIN4776 in the circumferential direction of a roller and the Rk ratio of the circumferential direction and axial direction of the roller on the surface of a conductive layer. CONSTITUTION: This developing roller 1 is constituted by forming the conductive layer 3 having an electrical conductivity on the outer periphery of a good conductive shaft 2. The nuclear depth roughness (Rk) stipulated in DIN4776 in the circumferential direction of the roller of the surface of this conductive layer 3 is 0.5 to 3.5μm and the Rk ratio of the circumferential direction and axial direction of the roller is the circumferential direction/axial direction > 0.1. A metallic shaft on which a mixture composed of various kinds of resins, etc., and conductive powder, magnetic powder, etc., or the shaft on which conductive resins, etc., are laminated and the surface of which is polished is usable as the conductive layer 3 when a photoreceptor and the developing roller 1 are contactless. On the other hand, a relatively soft elastic material is used for the need of a development nip when the photoreceptor and the developing roller 1 come into contact.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, with the progress of electrophotographic technology, there has been an increasing demand for a conductive member used in each electrophotographic process, and in particular, a developing roller used in a developing device has been attracting attention. The characteristic required for such a developing roller is not only a predetermined electric resistance value, but also a characteristic suitable for various developing mechanisms needs to be added.

Conventionally, as a developing method in the case of using a non-magnetic one-component developer as a developer (hereinafter referred to as toner), toner is supplied to a photosensitive drum holding a latent image to form a latent image on the photosensitive drum. A developing method (pressure developing method) in which a toner is attached to visualize a latent image is known. According to this method, since a magnetic material is unnecessary, the device can be simplified and downsized, and It is easy to color toner.

In this pressure developing method, a developing roller carrying toner is brought into contact with an electrostatic holding member holding an electrostatic latent image, such as a photosensitive drum, and toner is attached to the latent image on the electrostatic holding member. Therefore, it is necessary to form the developing roller with an elastic body having conductivity.

That is, in this pressure developing method, for example, as shown in FIG.
As shown in, the developing roller 1 is in contact with the photosensitive drum 5 between the toner applying roller 4 for supplying the toner and the photosensitive drum 5 holding the electrostatic latent image.
By rotating the developing roller 1, the photosensitive drum 5, and the toner applying roller 4 in the directions of the arrows in the drawing, the toner 6 is supplied to the surface of the developing roller 1 by the toner applying roller 4, and this toner is formed into a layering blade. 7 forms a uniform thin layer, and in this state, the developing roller 1 rotates while contacting the photosensitive drum 5, so that the toner formed in the thin layer adheres from the developing roller 1 to the latent image on the photosensitive drum 5. The latent image is visualized. In the figure, reference numeral 8 denotes a transfer section, which is adapted to transfer a toner image onto a recording medium such as paper, and 9 denotes a cleaning section, which is cleaned by a cleaning blade 10 on the surface of the photosensitive drum 5 after transfer. It is designed to remove the residual toner.

In this case, the developing roller 1 is the photosensitive drum 5
It is necessary to rotate while firmly maintaining the state of being in close contact with, and as shown in FIG. 1, silicone rubber is attached to the outer periphery of the shaft 2 made of a metal or other good conductive material.
An elastic rubber such as NBR or EPDM, an elastomeric material such as polyurethane, and a conductive layer 3 formed of an elastic body to which each sponge body or the like is mixed with a conductive agent to impart conductivity.

[0007]

However, the above-mentioned conventional developing roller, especially the developing roller composed of a single elastic layer, has the following drawbacks. 1. Elastic rubber such as silicone rubber, NBR, EPDM,
Alternatively, when the elastic layer is formed of an elastomeric material such as polyurethane, a slight difference in the surface state due to polishing causes a slight difference in the toner transport amount or the toner charge amount, and in some cases, an image defect occurs. .

The present invention has been made in view of the above circumstances, and by improving the surface condition of the roller, the toner conveyance amount or toner charge amount is made constant, and a high-quality image can be stably obtained. The purpose is to provide.

[Means and Actions for Solving the Problems]

The developing roller according to claim 1 of the present invention is a developing roller having a conductive layer formed on the outer periphery of a good conductive shaft, wherein the surface of the conductive layer is DIN4 in the roller circumferential direction.
776 standard core depth roughness (Rk) 0.5-3.5 μm
And the Rk ratio between the roller circumferential direction and the axial direction is circumferential direction / axial direction> 1.0.

Further, the developing roller according to claim 2 of the present invention is characterized in that the surface is formed by polishing the developing roller.

As a result of earnest studies on the surface condition of the developing roller, the present inventors found that the surface of the conductive layer had a DIN 4776 standard core depth roughness (Rk) of 0.
5 to 3.5 μm, and the Rk ratio in the roller circumferential direction and the axial direction is circumferential direction / axial direction> 1.0,
It was found that a high-quality image can be stably obtained by keeping the toner conveyance amount and further the toner charge amount constant.

That is, when the amount of developer conveyed on the roller is secured by providing minute irregularities on the roller surface, if the irregularities are too large, the amount of toner conveyed increases, but the toner charge amount is non-uniform. It will be something like. On the other hand, if the unevenness is too small, the toner conveyance amount cannot be secured,
Further, since the triboelectrification hardly occurs, a desired toner charge amount cannot be obtained. In these cases, a printing member is sometimes defective as an image defect. Therefore, the inventors of the present invention have found that optimum conditions exist in order to stably obtain a high-quality image in the surface state of the developing roller, and have arrived at the present invention.

The present invention will be described in more detail below. In the developing roller of the present invention, as shown in FIG. 1, a conductive layer 3 having conductivity is formed on the outer periphery of a good conductive shaft 2. Here, as the shaft 2, any one can be used as long as it has good conductivity, but normally, a metal core made of a solid metal body or a metal cylinder hollow inside is used. A metal shaft such as a body is used.

As the conductive layer 3, in the case where the photosensitive member and the developing roller are not in contact with each other, various resins or the like mixed with conductive powder, magnetic powder or the like, or a conductive resin is laminated on the surface of the metal shaft, What was polished can be used. On the other hand, when the photoconductor and the developing roller are in contact with each other, a relatively soft elastic body is used because of the necessity of the developing nip.

As the conductive layer 3, an elastomer such as conductive rubber or polyurethane or a foam material can be used as a base material.

First, the case where the conductive layer 3 is a conductive rubber will be described. In this case, as the rubber material forming the non-foamed conductive rubber, nitrile butadiene rubber, natural rubber, butyl rubber, nitrile rubber, isoprene rubber, polybutadiene rubber, silicone rubber, styrene-butadiene rubber, ethylene-propylene rubber, ethylene- Ordinary rubber such as propylene-diene terpolymer rubber (EPDM), chloroprene rubber, acrylic rubber, polynorbornene rubber or styrene-butadiene-styrene (SB
S), styrene-butadiene-styrene hydrogenated product (SEB
It is possible to use thermoplastic rubbers such as S) and mixtures thereof. Further, as the foamed conductive rubber, ethylene-propylene-diene terpolymer rubber (EPD) is used.
M), chloroprene rubber, chlorosulphonated polyethylene mixed with a conductive material, epichlorohydrin-ethylene oxide copolymer rubber foam or epichlorohydrin-ethylene oxide copolymer rubber mixed with a conductive material is preferable. Can be used for

As the conductive material to be blended with these rubber compositions, powdery materials will be exemplified first with conductive carbon such as Ketjenblack EC and acetylene black, and SA.
F, ISAF, HAF, FEF, GPF, SRF, F
Carbon for rubber such as T and MT, carbon for color (ink) that has been subjected to oxidation treatment, pyrolytic carbon, natural graphite, artificial graphite, antimony-doped tin oxide, titanium oxide, zinc oxide, nickel, copper, silver, Examples thereof include metals such as germanium and metal oxides, and conductive polymers such as polyaniline, polypyrrole, and polyacetylene. The compounding amount thereof may be 3 to 100 parts by weight, particularly 5 to 50 parts by weight, based on 100 parts by weight of all rubber components, whereby the volume resistivity of the conductive layer 3 is 10 ² to 10 parts by weight.
It can be adjusted to ¹⁰ Ω · cm.

Next, the case where the conductive layer 3 is polyurethane will be described. In this case, the polyurethane foam or elastomer may be any one produced by various methods, for example, a method of blending carbon black into a polyurethane prepolymer and subjecting the prepolymer to a crosslinking reaction, and blending a conductive material with a polyol. The polyol can be obtained by a method such as a method of reacting this polyol with polyisocyanate by a one-shot method.

The urethane used as the base material when the conductive layer 3 is polyurethane is a polyhydroxyl compound, which is a polyol used for producing general flexible polyurethane foams and urethane elastomers, for example, having a polyhydroxyl group at the terminal. In addition to polyether polyols, polyester polyols, and polyether polyols that are copolymers of both,
A general polyol such as a polyolefin polyol such as polybutadiene polyol or polyisoprene polyol, or a so-called polymer polyol obtained by polymerizing an ethylenically unsaturated monomer in the polyol can be used. Further, as the polyisocyanate compound, similarly, polyisocyanates used for producing general flexible polyurethane foams and urethane elastomers, that is, tolylene diisocyanate (TDI), crude TDI, 4,4-diphenylmethane diisocyanate (MDI), crude MD
I, an aliphatic polyisocyanate having 2 to 18 carbon atoms, an alicyclic polyisocyanate having 4 to 15 carbon atoms, and a mixture or modified product of these polyisocyanates, for example, a prepolymer obtained by partially reacting with a polyol Is used.

As the conductive material to be blended with these polyurethanes, the same conductive material as in the case of the above rubber composition and an ionic conductive material composed of an inorganic ionic substance such as lithium perchlorate or an organic ionic substance such as quaternary ammonium salt are used. Materials, cationic surfactants, anionic surfactants, amphoteric ion surfactants such as various betaines, and nonionic antistatic agents such as hydrophilic polyethers and polyesters may be used in combination. In the case of urethane, it is also preferable that the polyol component is prepolymerized with isocyanate.
The blending amount is 0.5 to 100 parts by weight of urethane.
It can be 50 parts by weight, particularly 1 to 30 parts by weight, whereby the volume resistivity of the conductive layer 3 is 10 ² to 10 ¹⁰ Ω.
It can be adjusted to cm. Other conductive materials include tetracyanoethylene, tetracyanoquinodimethane,
Benzoquinone, chloranil, anthraquinone, anthracene, dichlorodicyanobenzoquinone, ferrocene,
An electron accepting substance capable of forming a charge transfer complex such as phthalocyanine can be blended, and the blending amount in that case is 0.001 to 20 parts by weight, particularly 0.01 to 1 part by weight, relative to 100 parts by weight of urethane. Can be

The hardness of the conductive layer 3 is not particularly limited,
According to JIS-A scale, it is preferably 60 ° or less, particularly 10 to 55 °. In this case, if the hardness exceeds 60 °, the contact area with the photosensitive drum and the like may be small, and good development may not be performed. On the contrary, if the hardness is too low, the compression set becomes large, and the development may be difficult for some reason. When the roller is deformed or eccentric, uneven density of the image occurs. Therefore, even when the hardness of the elastic layer is low, the compression set is preferably as small as possible, specifically 20% or less.

The method for forming fine irregularities on the surface of the conductive layer 3 is not particularly limited and generally includes a polishing method such as a wet method or a dry method. In the present invention, the dry method is preferably used. FIG. 3 shows an example of the polishing method of the developing roller of the present invention. The developing roller 1 rotates in the direction of the arrow at about 5 m / min, and the grindstone 11 reaches 1500 m / min in the direction of the arrow.
Polishing is performed by rotating the roller at a certain speed and moving from one end side to the other end side of the roller while contacting the roller. In the present invention, in addition to the above-described method in which the grindstone moves, it is also possible to grind in a batch without moving the grindstone with a wider width. Further, a polishing method by a wet method in which a lubricant such as water or oil is sprayed between the grindstone and the conductive layer can be used.

As another forming method, for example, a method in which minute irregularities are formed on the inner surface of the mold in advance and a base material is injected into this to form a developing roller (injection molding method or the like) may be used. You can

The direction of surface roughness of the present invention will be described with reference to the schematic view of FIG. The DIN4776 standard core depth roughness (Rk) in the rotation direction of the developing roller is a value obtained by sweeping the surface of the conductive layer in the direction (1) of FIG. 4 using a contact type surface roughness meter described later. That is. On the other hand, the DIN 4776 standard core depth roughness (Rk) in the axial direction is a value obtained by sweeping at right angles to the direction (2) in FIG. 4, that is, the direction (1).

The surface roughness of the roller obtained by the above-mentioned measuring method is such that the DIN 4776 standard core depth roughness (Rk) in the roller circumferential direction is 0.5 to 3.5 μm, and the roller circumferential direction and the axial direction are the same. It is preferable that the Rk ratio of is in the circumferential direction / axial direction> 1.0.

When the surface roughness of the roller is too large, the toner conveyance amount increases, and the toner layer on the roller becomes thick. Since the toner particles themselves are charged, the charge of the toner layer as a whole increases as the thickness of the toner layer increases, so a high surface potential should be exhibited in the toner surface layer close to the photoconductor. Becomes
That is, in the developing process, when a predetermined developing bias is applied to the developing roller to cause the toner to fly to the photoconductor, the charge of the entire toner layer becomes excessive. It becomes a potential.

As a result, in some cases, for example, in the reversal development process, the developing roller surface potential does not fall between the dark decay potential and the charging potential on the photoconductor and becomes a high potential higher than the photoconductor charging potential. The so-called image fogging (hereinafter, referred to as HC
(Referred to as fogging) will occur.

On the other hand, if the surface roughness of the roller is too small, a predetermined toner conveyance amount cannot be secured, and frictional charging hardly occurs, so that a predetermined toner charge amount cannot be obtained. Therefore, weakly charged / reversely charged toner is generated in the conveyed toner, and in the case of reversal development, for example, a background fog occurs, which flies to a white print portion.

The developing roller of the present invention can be incorporated in an ordinary developing device using a magnetic or non-magnetic one-component developer. Specifically, as shown in FIG. 2, for applying toner for supplying toner. Between the roller 4 and the photosensitive drum 5 holding the electrostatic latent image, the developing roller 1 of the present invention is not in contact with or in contact with the photosensitive drum 5, and is in contact with or slightly apart from the toner applying roller 4. The developing roller 1, the photosensitive drum 5, and the toner applying roller 4 which are provided are respectively rotated in the directions of the arrows in the drawing, so that the toner 6
Is supplied to the surface of the developing roller 1 by the toner applying roller 4, the toner is adjusted to a uniform thin layer by the stratifying blade 7, and the developing roller 1 rotates in contact with the photosensitive drum 5 in this state. The toner formed in a thin layer adheres to the latent image on the photosensitive drum 5 from the developing roller 1 to visualize the latent image. Note that the details of FIG. 2 have been described in the related art, and thus description thereof will be omitted.

[0030]

The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. [Example 1] 100 parts of polyether polyol (OH number 33) (Exenol (registered trademark) 828 manufactured by Asahi Glass Co., Ltd.) having a molecular weight of 5000 by adding propylene oxide and ethylene oxide to glycerin MDI NCO% = 23% (Sumijour (registered trademark) PF manufactured by Sumitomo Bayer Urethane Co., Ltd.) 25.0 parts-1, 4-butanediol 2.5 parts-dibutyltin dilaurate 0.01 part-4th grade 0.25 parts of ammonium salt (KS-555 manufactured by Kao Corporation)

These were stirred and then poured into a mold heated to 110 ° C. and cured for 2 hours to form a conductive layer on the outer circumference of a metal shaft to obtain a developing roller. The surface of the obtained roller was dry-polished under the conditions shown in Table 1, and its surface condition,
Table 1 also shows the measured physical properties of the roller. The measurement conditions are shown below. (1) Surface condition Each roller was measured using a surface roughness meter Surfcom 570A type (manufactured by Tokyo Seimitsu Co., Ltd.). (2) Hardness A sheet-shaped sample manufactured under the same conditions as each roller was measured according to JIS-K6301 (A type). (3) Resistance Each roller is pressed against an aluminum flat plate with a load of 500 g on one side,
A DC voltage of 100 V was applied between the aluminum flat plate and the roller shaft, and the resistance was calculated from the current value flowing at that time.

[Example 2] A roller manufactured in the same manner as in Example 1 was polished under the conditions shown in Table 1, and the surface condition and the characteristic value of the roller were measured.

Comparative Example 1 The developing roller obtained with the composition of Example 1 was polished under the conditions shown in Table 1, and the surface condition and the roller characteristic value were measured.

Comparative Example 2 The developing roller obtained with the composition of Example 1 was abraded under the conditions of Table 1, and the surface condition and roller characteristic values were observed.

Comparative Example 3 The developing roller obtained with the composition of Example 1 was abraded under the conditions shown in Table 1 and the surface condition and roller characteristic values were observed.

[0036]

[Table 1]

The following image characteristic test and charging characteristic test were conducted on the developing rollers obtained in Examples 1 and 2 and Comparative Examples 1 to 3 above. Table 2 shows the results. (1) Image Each roller is installed as a developing roller in the developing unit shown in FIG. 2, and non-magnetic one-component toner having an average particle size of 7 μm is used, and reversal development is performed while rotating at a peripheral speed of 60 mm / sec in linear velocity. The image quality was evaluated by the following method, and the initial image quality (especially the following two image fogging) was evaluated. (A) HC fog A direct current voltage was applied to the blade in FIG. 2 and the fog generation potential was observed when the blade was swept negative. The more negative the generated potential, the better the HC fog. (B) Ground fog In FIG. 2, the developing bias was fixed to 0 V and the occurrence of ground fog was observed. At this time, the blade bias is
It was set to -100V. (C) Density unevenness The image quality obtained under the above conditions was visually evaluated. (2) Toner charge amount Each roller is installed as a developing roller in the developing unit portion shown in FIG. 2 and rotated at a peripheral speed of 50 mm / sec to form a uniform thin toner layer on the surface of the developing roller. Suction the thin layer with air and introduce it into the Faraday gauge,
It was determined by measuring the amount of charge. (3) Toner transport amount As in (2), a uniform thin toner layer is formed on the roller,
This thin toner layer was wiped off with a non-woven fabric of known weight, and the weight was measured.

[0038]

[Table 2]

[0039]

As described above, the present invention has a good adhesion due to its low hardness, has a stable toner conveyance amount, and provides a high-quality image free from uneven density and background fog. And a developing roller that is used. It can also be used for a charging roller, a transfer roller, etc., which require similar characteristics.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a developing roller showing an example of a conductive roller of the present invention.

FIG. 2 is a schematic sectional view showing an example of a developing device used by the roller of the present invention.

FIG. 3 is a schematic diagram showing an example of a polishing method of the present invention.

FIG. 4 is a schematic diagram in the direction of surface roughness of the present invention.

[Explanation of symbols]

 1 Developing Roller 2 Shaft 3 Conductive Layer 4 Toner Coating Roller 5 Photosensitive Drum (Latent Image Holding Body) 6 Toner (Non-Magnetic One-Component Developer) 7 Layering Blade 8 Transfer Section 9 Cleaning Section 10 Cleaning Blade 11 Grinding Stone

Claims (3)

[Claims] 1. A developing roller having a conductive layer formed on the outer periphery of a good conductive shaft, wherein the surface of the conductive layer has a DIN 4776 standard core depth roughness (Rk) in the roller circumferential direction.
Is 0.5 to 3.5 μm, and the Rk ratio in the roller circumferential direction and the axial direction is circumferential direction / axial direction> 1.0. 2. The developing roller according to claim 1, wherein the surface is formed by polishing the developing roller. 3. The latent image holding member, wherein the developing roller carries a non-magnetic one-component developer on the surface of an elastic body to form a thin film of the developer and holds an electrostatic latent image on the surface in this state. 2. A developing roller that contacts and visualizes the electrostatic latent image.
Alternatively, the developing roller according to claim 2.