JPH08179619A - Developing roller - Google Patents

Abstract

PURPOSE: To lower the friction resistance of a member in contact with a roller and to assure a stable toner transporting rate in initial period of printing so as to obtain high-grade images by subjecting the surface of a conductive layer to a surface treatment with finepowder having a specific particle size. CONSTITUTION: This developing roller 1 is constituted by forming a conductive layer 3 having an electrical conductivity on the outer periphery of a good conductive shaft 2. The surface of this conductive layer 3 is subjected to the surface treatment with the micropowder having an average particle size of <=30μm. In such a case, a metallic shaft 2 on which a mixture composed of various kinds of resins, etc., and conductive power, 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. Further, conductive rubber or elastomers, such as polyurethane, and foam materials are usable as the base material for the conductive layer 3.

Description

Detailed Description of the Invention

[0001]

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

[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 in which the shaft 2 is in close contact with, and therefore, 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 elastomer material such as polyurethane, a layer pressure regulating blade in contact with the developing roller,
Alternatively, the frictional resistance with the photoconductor is large, and when incorporated in an electrophotographic apparatus, there is a shake in driving, and density waviness called jitter occurs. 2. At the initial stage when the developing roller is installed, the toner conveyance amount becomes large, and sometimes an image defect occurs.

The present invention has been made in view of the above circumstances, and by adsorbing and holding a fine powder on the surface of the developing roller, the frictional resistance with a member in contact with the roller is reduced,
Further, another object of the present invention is to provide a developing roller capable of stably obtaining a high-quality image by ensuring a stable toner conveyance amount in the initial stage of printing.

[Means and Actions for Solving the Problems]

The developing roller according to claim 1 of the present invention is characterized in that the surface of the conductive layer is surface-treated with a fine powder having an average particle diameter of 30 μm or less.

Further, the developing roller according to claim 2 of the present invention is characterized in that the fine powder is a developer used in an electrophotographic process using the main developing roller.

The inventors of the present invention have earnestly studied the surface condition of the developing roller, and as a result, by surface-treating the surface of the conductive layer with fine powder having an average particle diameter of 30 μm or less,
It has been found that a high-quality image can be stably obtained by reducing the frictional resistance with a member in contact with the roller and by ensuring a stable toner conveyance amount in the initial stage of printing.

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, when the photosensitive member and the developing roller are not in contact with each other, various kinds of resin or the like mixed with conductive powder, magnetic powder, or conductive resin is laminated on 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.

For 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 a 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.

As the urethane used as the base material when the conductive layer 3 is polyurethane, as a polyhydroxyl compound, a polyol used in the production of general flexible polyurethane foam or urethane elastomer, for example, having a polyhydroxyl group at the end. 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.

The conductive material to be blended with these polyurethanes is 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 a quaternary ammonium salt. Materials, cationic surfactants, anionic surfactants, zwitterionic 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 fine powder to be adsorbed and retained on the surface of the conductive layer 3 is not particularly limited, and may have an average particle size of 30 μm or less, more preferably 3 to 30 μm.
Examples include charge control agents, silica, silicon, fluororesins, and the like. In particular, when toner is used as the fine powder, there is no problem even if the fine powder adsorbed and held is mixed in the toner box, and good developing characteristics can be obtained even in long-term operation, which is preferable. Used for. When a charge control agent is used for the fine powder, the toner charge amount can be controlled relatively arbitrarily depending on the charge polarity of the charge control agent used.

When the average particle diameter is 30 μm or more, the uneven gap due to the particles adsorbed and held on the surface becomes large, and the toner charge amount becomes uneven, so that an image defect occurs in a normal electrophotographic process. Will occur.

The method of surface treatment with fine powder is not particularly limited, but a sufficient effect can be obtained by rubbing the surface of the roller with a non-woven fabric containing fine powder.

When a fine powder is adsorbed and held on the surface, the friction coefficient of the roller surface is reduced, and when incorporated in an electrophotographic device, smooth driving is possible, and a high-quality image without jitter is obtained. To be

Also, in the initial stage, the amount of triboelectric charge between the roller and the toner is large, so that the toner carrying amount becomes large. However, by using this method, a stable toner carrying amount can be obtained even in the initial stage.

If the toner conveyance amount is too large, that is, the toner layer on the roller becomes thick, the following problems occur.

As the toner layer becomes thicker, the toner particles themselves are charged, so that the electric charge of the entire toner layer increases, so that a high surface potential is developed in the toner surface layer close to the photoreceptor. It will be. 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.
The surface layer has a high potential higher than the developing bias.

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. That is, so-called image fogging occurs, in which toner is ejected to a white printed portion.

The reason why the toner carrying amount is stabilized is that the surface state is smoothed by holding the fine powder and the physical initial toner carrying amount is lowered. Further, when toner is used as the fine powder, the toner is triboelectrically charged through the attracted and held toner, so that the toner charge amount is reduced. It is considered that this reduces the toner transport amount in the initial stage.

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, it is for toner application 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.

[0031]

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 polished to a predetermined surface condition. The toner (average particle diameter 10 μm) used in the electrophotographic apparatus was contained in a soft non-woven fabric so as not to damage the roller, and the roller was rubbed several times to adsorb and hold the toner on the roller.

[Embodiment 2] A negative charge control agent (CopyCharge manufactured by Hoechst) was added to a roller manufactured in the same manner as in Embodiment 1.
NEG VP2036) was adsorbed and retained in the same manner as in Example 1.

[Comparative Example 1] The developing roller obtained by the formulation of Example 1 was used as it was without holding fine particles.

With respect to the developing rollers obtained in Examples 1 and 2 and Comparative Example 1, the following image characteristic test and roller characteristic test were conducted. The results are shown in Table 1.

(1) Image Fogging 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 the roller is rotated at a peripheral speed of 60 mm / sec. The initial image quality (especially the image fog)
Was evaluated. (2) Roller surface potential Each roller was mounted 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. An external power source applied -500 V to this roller shaft, and the roller surface potential at that time was measured. (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. (4) Friction coefficient HEIDON-14 manufactured by HEIDON was used to measure the dynamic friction coefficient when friction was made perpendicular to the longitudinal direction of the roller, and the ratio in the roller of Comparative Example 1 was set to 1 and the ratio was displayed.

[0037]

[Table 1]

[0038]

As described above, the present invention provides a developing roller and a developing device having a stable toner conveyance amount and capable of obtaining a high-quality image without density unevenness or background fog. 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.

[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

Claims (2)

[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 is surface-treated with a fine powder having an average particle diameter of 30 μm or less. 2. The developing roller, wherein the fine powder is a developer used in an electrophotographic process using the main developing roller.