EP4621492A1

EP4621492A1 - Conductive member, charging device, process cartridge, and image forming apparatus

Info

Publication number: EP4621492A1
Application number: EP24195120.1A
Authority: EP
Inventors: Toshiyasu Yukawa; Kenta Yamakoshi; Yukimi Kawabata
Original assignee: Fujifilm Business Innovation Corp
Current assignee: Fujifilm Business Innovation Corp
Priority date: 2024-03-21
Filing date: 2024-08-19
Publication date: 2025-09-24
Also published as: CN120686558A; JP2025144849A

Abstract

In a conductive member, the percentage area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is 15% by area or more.

Description

Background

(i) Technical Field

The present disclosure relates to a conductive member, a charging device, a process cartridge, and an image forming apparatus.

(ii) Related Art

In Japanese Unexamined Patent Application Publication No. 2011-022410 , there is described a conductive member comprising a substrate, an elastic layer provided on the substrate, and a surface layer provided on the elastic layer, the surface layer having a sea-island structure composed of a sea portion containing a first resin and island portions containing a second resin and containing carbon black at least inside the island portions.

Summary

Accordingly, it is an object of the present disclosure to provide a conductive member that is superior in the reduction of the occurrence of color streaks compared with when the percentage area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is less than 15% by area or when the average area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is less than 0.05 µm².
According to a first aspect of the present disclosure, there is provided a conductive member, wherein a percentage area of particulate conductive portions measured when conductive points on a surface are measured by conductive atomic force microscopy is 15% by area or more.
According to a second aspect of the present disclosure, there is provided a conductive member, wherein an average area of particulate conductive portions measured when conductive points on a surface are measured by conductive atomic force microscopy is 0.05 µm² or more.
According to a third aspect of the present disclosure, there is provided a conductive member according to the first aspect, wherein the percentage area of the conductive portions is 15% by area or more and 80% by area or less.
According to a fourth aspect of the present disclosure, there is provided a conductive member according to the third aspect, wherein the percentage area of the conductive portions is 30% by area or more and 60% by area or less.
According to a fifth aspect of the present disclosure, there is provided a conductive member according to the first or second aspect, wherein the average area of the conductive portions is 0.05 µm² or more and 1.0 µm² or less.
According to a sixth aspect of the present disclosure, there is provided a conductive member according to the fifth aspect, wherein the average area of the conductive portions is 0.20 µm² or more and 0.50 µm² or less.
According to a seventh aspect of the present disclosure, there is provided a conductive member according to any one of the first to sixth aspects, wherein when a current value is measured on the surface while a 100-nm diameter probe is moved with -30 V applied thereto, 50-µm square regions in which a value of current flowing per segment is 60 pA or more, where the regions are each divided into a grid of 256 × 256 segments, constitute 60% by area or more.
According to an eighth aspect of the present disclosure, there is provided a conductive member according to any one of the first to seventh aspects, wherein the conductive member includes a substrate, an elastic layer provided on the substrate, and a surface layer provided on the elastic layer.
According to a ninth aspect of the present disclosure, there is provided a conductive member according to the eighth aspect, wherein the surface layer contains at least one first resin, at lease one second resin, and at least one conductive agent.
According to a tenth aspect of the present disclosure, there is provided a conductive member according to the ninth aspect, wherein the surface layer has a sea-island structure composed of a sea portion containing the first resin and island portions containing the second resin.
According to an eleventh aspect of the present disclosure, there is provided a charging device including the conductive member according to any one of the first to tenth aspects.
According to a twelfth aspect of the present disclosure, there is provided a process cartridge attachable to and detachable from an image forming apparatus, the process cartridge including the charging device according to the eleventh aspect.
According to a thirteenth aspect of the present disclosure, there is provided an image forming apparatus including an image carrier; the charging device according to the eleventh aspect that charges a surface of the image carrier; an electrostatic latent image forming device that forms an electrostatic latent image on the charged surface of the image carrier; a developing device that develops, using a developer containing toner, the electrostatic latent image on the surface of the image carrier to form a toner image; and a transfer device that transfers the toner image to a surface of a recording medium.
According to the first or eighth aspect of the present disclosure, there is provided a conductive member superior in the reduction of the occurrence of color streaks compared with when the percentage area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is less than 15% by area.
According to the second aspect of the present disclosure, there is provided a conductive member superior in the reduction of the occurrence of color streaks compared with when the average area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is less than 0.05 µm².
According to the third aspect of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than when the percentage area of the conductive portions is less than 15% by area or exceeds 80% by area.
According to the fourth aspect of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than when the percentage area of the conductive portions is less than 30% by area or exceeds 60% by area.
According to the fifth aspect of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than when the average area of the conductive portions is less than 0.05 µm² or exceeds 1.0 µm².
According to the sixth aspect of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than when the average area of the conductive portions is less than 0.20 µm² or exceeds 0.50 µm².
According to the seventh aspect of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than in the case in which when the current value is measured on the surface while a 100-nm diameter probe is moved with -30 V applied to it, 50-µm square regions in which the value of current flowing per segment is 60 pA or more, where the regions are each divided into a grid of 256 × 256 segments, constitute less than 60% by area.
According to the ninth or tenth aspect of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than when the surface layer contains only one type of resin.
According to the eleventh, twelfth, or thirteenth aspect of the present disclosure, there is provided a charging device, process cartridge, or image forming apparatus superior in the reduction of the occurrence of color streaks compared with when the conductive member included is one for which the percentage area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is less than 15% by area or the average area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is less than 0.05 µm².

Brief Description of the Drawings

Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein:

Fig. 1 is a schematic perspective view illustrating an example of a conductive member according to an exemplary embodiment;
Fig. 2 is a schematic cross-sectional view illustrating an example of a conductive member according to an exemplary embodiment and is a II-II cross-sectional view of Fig. 1; and
Fig. 3 is a schematic view illustrating the structure of an example of an image forming apparatus according to an exemplary embodiment.

Detailed Description

Exemplary embodiments as examples of the present disclosure will now be described. These descriptions and the Examples are intended to illustrate exemplary embodiments and not intended to limit the scope of the disclosure.
In a series of numerical ranges presented herein, an upper or lower limit specified in one numerical range may be substituted with the upper or lower limit of another numerical range in the same series. In a numerical range presented herein, furthermore, the upper or lower limit of the numerical range may be substituted with a value indicated in the Examples.
A constituent may include multiple substances corresponding to it.
When the amount of a constituent in a composition is mentioned, and if multiple substances corresponding to the constituent are present in the composition, the mentioned amount represents the total amount of the multiple substances present in the composition unless stated otherwise.

Conductive Member

In a first exemplary form of a conductive member according to an exemplary embodiment, the percentage area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is 15% by area or more.
In a second exemplary form of a conductive member according to an exemplary embodiment, the average area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is 0.05 µm² or more.
It should be noted that simply referring to "a/the conductive member according to an/this exemplary embodiment" without further limitation herein means that the statement pertains to both of the first and second exemplary forms described above. Simply referring to "conductive portions," "the surface layer," etc., without further limitation, furthermore, means that the statement pertains to the conductive portions, surface layer, etc., in both of the first and second exemplary forms described above.
The conductive member according to this exemplary embodiment is suitable for use as a charging member.
Known conductive members are disadvantageous in that particulate conductive portions on their surface are not sufficiently formed, resulting in the creation of charging defects and the occurrence of color streaks.
For the conductive member according to this exemplary embodiment, the percentage area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is 15% by area or more, or the average area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is 0.05 µm² or more; presumably because of this, a larger number of portions with a low resistance value are present on the surface, allowing the surface to be sufficiently charged and helping reduce the occurrence of color streaks.
The conductive member according to this exemplary embodiment will now be described in detail.

Percentage Area and Average Area of Particulate Conductive Portions

In the first exemplary form of the conductive member according to this exemplary embodiment, the percentage area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy (C-AFM) is 15% by area or more; for the reduction of the occurrence of color streaks and for lower resistance, the percentage area may be 15% by area or more and 80% by area or less, preferably 20% by area or more and 70% by area or less, more preferably 30% by area or more and 60% by area or less, even more preferably 30% by area or more and 50% by area or less.
In the second exemplary form of the conductive member according to this exemplary embodiment, the percentage area of particulate conductive portions measured when conductive points on the surface are measured by C-AFM may be 15% by area or more for the reduction of the occurrence of color streaks and for lower resistance; preferably, the percentage area is 15% by area or more and 80% by area or less, more preferably 20% by area or more and 70% by area or less, even more preferably 30% by area or more and 60% by area or less, still more preferably 30% by area or more and 50% by area or less.
In the second exemplary form of the conductive member according to this exemplary embodiment, the average area of particulate conductive portions measured when conductive points on the surface are measured by C-AFM is 0.05 µm² or more; for the reduction of the occurrence of color streaks and for lower resistance, the average area may be 0.05 µm² or more and 1.0 µm² or less, preferably 0.10 µm² or more and 0.80 µm² or less, more preferably 0.20 µm² or more and 0.50 µm² or less, even more preferably 0.30 µm² or more and 0.40 µm² or less.
In the first exemplary form of the conductive member according to this exemplary embodiment, the average area of particulate conductive portions measured when conductive points on the surface are measured by C-AFM may be 0.05 µm² or more for the reduction of the occurrence of color streaks and for lower resistance; preferably, the average area is 0.05 µm² or more and 1.0 µm² or less, more preferably 0.10 µm² or more and 0.80 µm² or less, even more preferably 0.20 µm² or more and 0.50 µm² or less, still more preferably 0.30 µm² or more and 0.40 µm² or less.
In this exemplary embodiment, the method for measuring conductive points on the surface of the conductive member by conductive atomic force microscopy (C-AFM) is as follows.
On the surface of the conductive member, conductive points are measured under the conditions specified below using AFM5200S (AFM/Current), manufactured by Hitachi High-Tech Corporation, and a CL scanner (110 µm) for S-image. Portions with 60 pA or more are defined as conductive portions, and the percentage area and average area of conductive portions measured in the shape of particles are calculated.

Probe holder: Multi-holder
Cantilever: SI-DF20-R (100 nm)
Bias voltage: -10 V
Scan range: 50 µm × 50 µm
Number of data points: X, 512; Y, 512

For the conductive member according to this exemplary embodiment, when the current value is measured on the surface while a 100-nm diameter probe is moved with -30 V applied to it, 50-µm square (= 50 µm × 50 µm) regions in which the value of current flowing per segment is 60 pA or more, where the regions are each divided into a grid of 256 × 256 segments, may constitute 60% by area or more for the reduction of the occurrence of color streaks; preferably, the percentage of such regions is 60% by area or more and 90% by area or less, more preferably 60% by area or more and 80% by area or less, even more preferably 65% by area or more and 75% by area or less.
For the conductive member according to this exemplary embodiment, furthermore, regions in which the value of current flowing per segment, the segment being as defined above, is 60 pA or more and 100 pA or less may constitute 60% by area or more for the reduction of the occurrence of color streaks; preferably, the percentage of such regions is 60% by area or more and 90% by area or less, more preferably 60% by area or more and 80% by area or less, even more preferably 65% by area or more and 75% by area or less.
In this exemplary embodiment, the method for measuring regions in which the current value is 60 pA or more on the surface of the conductive member is as follows.
On the surface of the conductive member obtained, 50-µm square areas are each divided into a grid of 256 × 256 segments, and the value of current flowing in each segment is measured using the aforementioned conductive atomic force microscope while a 100-nm diameter probe (cantilever) is moved with -30 V applied to it. The other measurement conditions are set to the same as in the method for measuring conductive points described above.
The conductive member according to this exemplary embodiment may include, for chargeability and the ease of fabrication, a substrate, an elastic layer provided on the substrate, and a surface layer provided on the elastic layer.
The surface layer of the conductive member according to this exemplary embodiment, furthermore, may contain at least one first resin, at least one second resin, and at least one conductive agent for the ease of formation of particulate conductive portions.
Moreover, the surface layer of the conductive member according to this exemplary embodiment may have, for the ease of formation of particulate conductive portions, a sea-island structure composed of a sea portion containing the first resin and island portions containing the second resin.
Fig. 1 is a schematic perspective view illustrating an example of a conductive member according to this exemplary embodiment. Fig. 2 is a schematic cross-sectional view illustrating an example of a conductive member according to this exemplary embodiment. Fig. 2 is a II-II cross-sectional view of Fig. 1.
As illustrated in Figs. 1 and 2, a conductive member 121A according to this exemplary embodiment is, for example, a roller-shaped member having a shaft 30 (an example of a substrate), an elastic layer 31 disposed on the outer circumferential surface of the shaft 30, and a surface layer 32 disposed on the outer circumferential surface of the elastic layer 31.
Each component of the conductive member according to this exemplary embodiment will now be described in detail. The numerals assigned to the individual components, however, may be omitted.

Substrate

The conductive member according to this exemplary embodiment may include a substrate.
The substrate may be a cylindrical or columnar member that is conductive. In this context, conductive means that the volume resistivity is less than 10¹³ Ω cm.
Examples of materials for the substrate include metals, such as iron (e.g., free-cutting steel), copper, brass, stainless steel, aluminum, and nickel. A member (e.g., a resin or ceramic member) that has been subjected to plating treatment on its outer circumferential surface and a member (e.g., a resin or ceramic member) in which a conductive agent has been dispersed are also examples of substrates.

Elastic Layer

The conductive member according to this exemplary embodiment may include an elastic layer provided on the substrate.
The elastic layer may contain, for example, an elastic material and at least one conductive agent and may further contain other additives.
Examples of elastic materials include isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, polyurethane, silicone rubber, fluorine rubber, styrenebutadiene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, ethylene-propylene-diene ternary copolymer rubber (EPDM), acrylonitrile-butadiene copolymer rubber (NBR), natural rubber, and blend rubbers made therefrom. Polyurethane, silicone rubber, EPDM, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, NBR, and blend rubbers made therefrom may be used in particular. Such elastic materials may be of foam type or nonfoam type.
Examples of conductive agents include electron-conducting agents and ion-conducting agents. Examples of electron-conducting agents include powders of materials such as carbon blacks, e.g., Ketjenblack and acetylene black; pyrolytic carbon and graphite; conductive metals or alloys, e.g., aluminum, copper, nickel, and stainless steel; conductive metal oxides, e.g., tin oxide, indium oxide, titanium oxide, tin oxide-antimony oxide solid solution, and tin oxide-indium oxide solid solution; and insulating substances whose surfaces have been subjected to conduction treatment. Examples of ion-conducting agents include perchlorates or chlorates of oniums, such as tetraethylammonium and lauryltrimethylammonium; and perchlorates or chlorates of alkali metals or alkaline earth metals, such as lithium and magnesium. One conductive agent may be used alone, or two or more may be used in combination.
Specific examples of carbon blacks include "SPECIAL BLACK 350," "SPECIAL BLACK 100," "SPECIAL BLACK 250," "SPECIAL BLACK 5," "SPECIAL BLACK 4," "SPECIAL BLACK 4A," "SPECIAL BLACK 550," "SPECIAL BLACK 6," "COLOUR BLACK FW200," "COLOUR BLACK FW2," and "COLOUR BLACK FW2V," all manufactured by Orion Engineered Carbons S.A., and "MONARCH 880," "MONARCH 1000," "MONARCH 1300," "MONARCH 1400," "MOGUL-L," and "REGAL 400R," all manufactured by Cabot Corporation.
For the amount of conductive agent blended, there is no specific restriction; however, in the case of electron-conducting agents, the amount blended may fall within the range of 1 part by mass to 30 parts by mass, preferably falling within the range of 15 parts by mass to 25 parts by mass, in relation to 100 parts by mass of the elastic material. In the case of ion-conducting agents, the amount blended may fall within the range of 0.1 parts by mass to 5.0 parts by mass, preferably falling within the range of 0.5 parts by mass to 3.0 parts by mass, in relation to 100 parts by mass of the elastic material.
Examples of other additives blended into the elastic layer include common materials that can be blended into an elastic layer, such as softeners, plasticizers, curing agents, vulcanizing agents, vulcanization accelerators, antioxidants, surfactants, coupling agents, and fillers (e.g., silica and calcium carbonate).
The thickness of the elastic layer may be approximately 1 mm or more and 15 mm or less, preferably approximately 2 mm or more and 10 mm or less, on average.
The volume resistivity of the elastic layer may be 10³ Ω·cm or more and 10¹⁴ Ω·cm or less.

Surface Layer

The conductive member according to this exemplary embodiment may include a surface layer; preferably, the conductive member includes a surface layer provided on the elastic layer.

Composition of the Surface Layer

The surface layer may contain at least one first resin, at least one second resin, and at least one conductive agent for the ease of formation of particulate conductive portions; preferably, the surface layer has a sea-island structure composed of a sea portion containing at least one first resin and island portions containing at least one second resin and also contains at least one conductive agent.
In this context, "sea-island structure" refers to a structure in which at least two types of resins coexist in a mutually immiscible state and in which island portions, which constitute a dispersed phase, are enclosed within a sea portion, which is a continuous phase.
The sea-island structure is formed through the adjustment of the difference in solubility parameter (SP value) between the first resin and the second resin and the mix ratio between the first resin and the second resin. The difference in SP value between the first resin and the second resin may be 2 or greater and 10 or less because this facilitates the formation of a sea-island structure.
The mix ratio between the first resin and the second resin will be described later herein.
The method for calculating the solubility parameter (SP value) is the method described in VII 680 to 683 of "Polymer Handbook Fourth Edition John Wiley & Sons." The solubility parameters of typical resins are presented in VII 702 to 711 of the same publication.
Examples of first resins include acrylic resins, cellulose resins, polyamide resins, copolymer nylons, polyurethane resins, polycarbonate resins, polyester resins, polyethylene resins, polyvinyl resins, polyarylate resins, styrene butadiene resins, melamine resins, epoxy resins, urethane resins, silicone resins, fluoropolymers (e.g., tetrafluoroethylene perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, and polyvinylidene fluoride), and urea resins. Copolymer nylons are copolymers containing any one type or multiple types selected from nylon 610, nylon 11, and nylon 12 as their polymerization units and may contain, for example, nylon 6 or nylon 66 as other polymerization units. As the first resin, the elastic material blended into the elastic layer may be used. One type of resin may be used alone as the first resin, or two or more types of resins may be used in combination.
The first resin may be a polyamide resin (e.g., nylon) for reasons such as electrical properties or contamination resistance of the surface layer; adequate hardness or the maintenance of the surface layer, because the surface layer is provided on an elastic layer; and the dispersibility of the conductive agent or the ability to form a coating when a dispersion is used to form the surface layer; preferably, the first resin is a methoxymethylated polyamide resin (e.g., methoxymethylated nylon).
Examples of second resins include polyvinyl butyral resins, polystyrene resins, and polyvinyl alcohol. One type of resin may be used alone as the second resin, or two or more types of resins may be used in combination.
The second resin may be a polyvinyl butyral resin for reasons such as electrical properties or contamination resistance of the surface layer; adequate hardness or the maintenance of the surface layer, because the surface layer is provided on an elastic layer; and the dispersibility of the conductive agent or the ability to form a coating when a dispersion is used to form the surface layer.
The amount of the second resin may be 10 parts by mass or more and 30 parts by mass or less, preferably 12 parts by mass or more and 28 parts by mass or less, more preferably 15 parts by mass or more and 25 parts by mass or less in relation to a total of 100 parts by mass of the first and second resins.
When the amount of the second resin is set to 10 parts by mass or more and 30 parts by mass or less in relation to a total of 100 parts by mass of the first and second resins, the conductive member is one with which the occurrence of color streaks in the axial direction that occur during image formation is further reduced. A possible reason is as follows.
When the amount of the second resin is set to 10 parts by mass or more in relation to a total of 100 parts by mass of the first and second resins, the occupancy of the surface layer by the island portions is high. The number of conduction paths within the surface layer, therefore, further increases. When the amount of the second resin is set to 30 parts by mass or less in relation to a total of 100 parts by mass of the first and second resins, furthermore, it is more likely that the island portions are present dispersed within the surface layer in a nearly uniform state by virtue of not too high an occupancy of the surface layer by the island portions.
The total amount of the first and second resins may be 50% by mass or more and 95% by mass or less in relation to the entire surface layer; preferably, the total amount is 60% by mass or more and 90% by mass or less, more preferably 70% by mass or more and 85% by mass or less.
Examples of conductive agents include electron-conducting agents and ion-conducting agents. Examples of electron-conducting agents include powders of materials such as carbon blacks, e.g., Ketjenblack and acetylene black; pyrolytic carbon and graphite; conductive metals or alloys, e.g., aluminum, copper, nickel, and stainless steel; conductive metal oxides, e.g., tin oxide, indium oxide, titanium oxide, tin oxide-antimony oxide solid solution, and tin oxide-indium oxide solid solution; and insulating substances whose surfaces have been subjected to conduction treatment. Examples of ion-conducting agents include perchlorates or chlorates of oniums, such as tetraethylammonium and lauryltrimethylammonium; and perchlorates or chlorates of alkali metals or alkaline earth metals, such as lithium and magnesium. One conductive agent may be used alone, or two or more may be used in combination.
The conductive agent may be carbon black.
When carbon black is used as the conductive agent, it is more likely that the conductive member is one with which the occurrence of color streaks in the axial direction that occur during image formation is reduced. A possible reason is as follows.
Carbon black is likely to concentrate near the regions of the island portions in the surface layer compared with conductive agents other than carbon black. When the occupancy by area by the island portions is set to 10% or more and 45% or less or when the diameter of the island portions is set to 100 nm or more and 750 nm or less, therefore, the advantage of increased conduction paths in the surface layer is further enhanced.
Presumably for this reason, using carbon black as the conductive agent makes it more likely that the conductive member is one with which the occurrence of color streaks in the axial direction that occur during image formation is reduced.
Examples of carbon blacks include Ketjenblack, acetylene black, and oxidized carbon black with a pH of 5 or lower. More specific examples include "SPECIAL BLACK 350," "SPECIAL BLACK 100," "SPECIAL BLACK 250," "SPECIAL BLACK 5," "SPECIAL BLACK 4," "SPECIAL BLACK 4A," "SPECIAL BLACK 550," "SPECIAL BLACK 6," "COLOUR BLACK FW200," "COLOUR BLACK FW2," and "COLOUR BLACK FW2V," all manufactured by Orion Engineered Carbons S.A., and "MONARCH 880," "MONARCH 1000," "MONARCH 1300," "MONARCH 1400," "MOGUL-L," and "REGAL 400R," all manufactured by Cabot Corporation.
The average particle diameter of the carbon black may be 15 nm or more and 30 nm or less, preferably 15 nm or more and 25 nm or less, more preferably 15 nm or more and 20 nm or less.
When the average particle diameter of the carbon black is set to 15 nm or more and 30 nm or less, it is more likely that the conductive member is one with which the occurrence of color streaks in the axial direction that occur during image formation is reduced. A possible reason is as follows.
When the average particle diameter of the carbon black is set to 15 nm or more and 30 nm or less, the particles of the carbon black are present more densely and are more likely to concentrate near the regions of the island portions in the surface layer. As a result, it is easier for electric current to flow between the particles of the conductive agent. When the occupancy by area by the island portions is set to 10% or more and 45% or less or when the diameter of the island portions is set to 100 nm or more and 750 nm or less, therefore, the advantage of increased conduction paths in the surface layer is further enhanced.
Presumably for this reason, it is more likely that the conductive member is one with which the occurrence of color streaks in the axial direction that occur during image formation is reduced.
The average particle diameter of the carbon black is a value measured using a TEM (transmission electron microscope).
The measurement method is as follows.
First, the surface layer is cut using a microtome, and the resulting cross-section is observed using a TEM (transmission electron microscope). The diameters of circles having areas equal to the projected areas of 50 carbon black particles are measured as particle diameters, and their average is reported as the average particle diameter.
The amount of the conductive agent may be 10 parts by mass or more and 15 parts by mass or less in relation to a total of 100 parts by mass of the first and second resins.
When the amount of the conductive agent is set to 10 parts by mass or more and 15 parts by mass or less in relation to a total of 100 parts by mass of the first and second resins, it is more likely that the conductive member is one with which the occurrence of color streaks in the axial direction that occur during image formation is reduced. Possible reasons are as follows.
When the amount of the conductive agent is set to 10 parts by mass or more in relation to a total of 100 parts by mass of the first and second resins, the amount of conductive agent contained in the surface layer is large. It becomes easier for the particles of the conductive agent to be in a state in which they are close to each other, allowing for smoother flow of electric current between the particles of the conductive agent. When the occupancy by area by the island portions is set to 10% or more and 45% or less or when the diameter of the island portions is set to 100 nm or more and 750 nm or less, therefore, the advantage of increased conduction paths in the surface layer is further enhanced.
When the amount of the conductive agent is set to 15 parts by mass or less in relation to a total of 100 parts by mass of the first and second resins, it is less likely that the conductive agent is interspersed throughout the sea portion contained in the surface layer, reducing the likelihood of a decrease in conduction effect due to dispersed conduction paths.
Presumably for these reasons, it is more likely that the conductive member is one with which the occurrence of color streaks in the axial direction that occur during image formation is reduced.
The surface layer may further contain a silicon-containing compound.
The amount of the silicon-containing compound may be 0.05 parts by mass or more and 0.15 parts by mass or less in relation to a total of 100 parts by mass of the first and second resins.
When the surface layer further contains a silicon-containing compound and when the amount of the silicon-containing compound is set to 0.05 parts by mass or more and 0.15 parts by mass or less in relation to a total of 100 parts by mass of the first and second resins, the occurrence of color streaks in the axial direction that occur during image formation is reduced. The contamination resistance and fog reduction effect of the conductive member, furthermore, improve. A possible reason is as follows.
When the amount of the silicon-containing compound is set to 0.05 parts by mass or more in relation to a total of 100 parts by mass of the first and second resins, the contamination resistance and fog reduction effect of the conductive member improve as a result of the surface roughness of the surface layer decreasing to an adequate level. When the amount of the silicon-containing compound is set to 0.15 parts by mass or less in relation to a total of 100 parts by mass of the first and second resins, furthermore, the resistance of the surface layer decreases.
The amount of the silicon-containing compound may be 0.075 parts by mass or more and 0.125 parts by mass or less, preferably 0.09 parts by mass or more and 0.11 parts by mass or less, in relation to a total of 100 parts by mass of the first and second resins.
The amount of the silicon-containing compound is measured using an XPS (x-ray photoelectron spectrometer). As the x-ray photoelectron spectrometer, ESCA-3400 (product name), manufactured by Shimadzu Corporation, for example, can be used.
In the following, the procedure for measuring the amount of the silicon-containing compound will be described.
The Si element is detected based on the positions of photoelectron peaks caused by x-ray excitation, and quantification is performed based on the area intensity of each peak.
As for the total mass of the first and second resins, it is calculated by determining the blending percentages of the first and second resins based on the ratio between the peaks for C=O and N-H derived from amide linkages contained in the first resin and CO derived from butyral groups contained in the second resin as detected by FT-IR (Fourier-transform infrared spectroscopy). As the FT-IR system, IRSpirit (product name), manufactured by Shimadzu Corporation, for example, can be used.
Examples of silicon-containing compounds include silicone oils, such as dimethylpolysiloxane, diphenylpolysiloxane, and phenylmethylpolysiloxane; and modified silicone oils, such as polyether-modified polysiloxanes, amino-modified polysiloxanes, epoxy-modified polysiloxanes, carboxyl-modified polysiloxanes, carbinol-modified polysiloxanes, fluorine-modified polysiloxanes, methacrylic-modified polysiloxanes, mercapto-modified polysiloxanes, and phenol-modified polysiloxanes.
For miscibility reasons, the silicon-containing compound may be a polyether-modified polysiloxane.
The surface layer may contain other additives.
As other additives blended into the surface layer, known ones are used; examples include acid catalysts, softeners, plasticizers, curing agents, vulcanizing agents, vulcanization accelerators, antioxidants, surfactants, coupling agents, and fillers (e.g., porous polyamide, silica, and calcium carbonate).

Percentage Areas of the Island Portions

When a cross-section of the surface layer is observed, the percentage area A of the island portions in the region A from the surface of the surface layer to a depth of 20% of the thickness is 25% or more and 45% or less. For the reduction of a decrease in mechanical strength and the reduction of the occurrence of color streaks, percentage area A of the island portions may be 30% or more and 40% or less, preferably 35% or more and 40% or less.
When the percentage area of the island portions in the entire surface layer falls within an appropriate range, mechanical strength is maintained, yet it is more likely that the occurrence of color streaks is reduced.
When a cross-section of the surface layer is observed, therefore, the percentage area B of the island portions in the region B deeper than 20% of the thickness from the surface of the surface layer may be 40% or more and 50% or less for the reduction of a decrease in mechanical strength and the reduction of the occurrence of color streaks; preferably, percentage area B is 42.5% or more and 50% or less, more preferably 45% or more and 50% or less.
The difference between percentage area A of the island portions and percentage area B of the island portions, furthermore, may be 15% or less as an absolute value for the reduction of a decrease in mechanical strength and the reduction of the occurrence of color streaks; preferably, the difference is 10% or less, more preferably 5% or less.
The percentage areas of the island portions are values measured as follows.
By cryomicrotomy, a slice specimen of the surface layer cut in the thickness direction is prepared. On this slice specimen, the cross-section of the surface layer created by cryomicrotomy is observed using a scanning electron microscope.
Then, in the observation image, the area of the region corresponding to region A, from the surface of the surface layer to a depth of 20% of the thickness, and the area of the island portions in region A are measured. The percentage of the area of the island portions in region A to the area of the region corresponding to region A is calculated as percentage area A of the island portions.
Likewise, the area of the region corresponding to region B, deeper than a depth of 20% of the thickness from the surface of the surface layer, and the area of the island portions in region B are measured, and the percentage of the area of the island portions in region B to the area of the region corresponding to region B is calculated as percentage area B of the island portions.

Diameter of the Island Portions

For the conductive member according to this exemplary embodiment, the diameter of the island portions on a cross-section of the surface layer (cross-section in any of region A or B) may be 100 nm or more and 750 nm or less, preferably 150 nm or more and 650 nm or less, more preferably 200 nm or more and 600 nm or less, even more preferably 300 nm or more and 400 nm or less.
The diameter of the island portions is a value measured as follows.
By cryomicrotomy, a slice specimen of the surface layer cut in the thickness direction is prepared. On this slice specimen, the cross-section of the surface layer created by cryomicrotomy is observed using a scanning electron microscope. Any ten island portions are selected. For each of the ten island portions, the longest length of a line segment drawn between any two points on the outline of the island portion (the so-called major axis) is measured; the average of the ten major axes is reported as the diameter (nm) of the island portions.

Surface Roughness Rz of the Outer Circumferential Surface of the Surface Layer

The surface roughness Rz of the outer circumferential surface of the surface layer may be 8.0 µm or less.
Usually, when the surface roughness Rz of the outer circumferential surface of the surface layer exceeds 5.0 µm, fogging is likely to occur. With the conductive member according to this exemplary embodiment, however, the occurrence of fogging is reduced even when the surface roughness Rz of the outer circumferential surface of the surface layer exceeds 5.0 µm, as long as it is 8.0 µm or less.
The surface roughness Rz is measured using a contact surface roughness gauge (SURFCOM 570A, manufactured by Tokyo Seimitsu Co., Ltd.) and a stylus having a diamond tip (a 5-µmR, 90° cone) in an environment with a temperature of 23°C and a relative humidity of 55%. The measured distance is 2.5 mm, and the measurement sites are between the points of 5 mm and 7.5 mm from the ends of the discharging region. Measurements are taken at four points spaced at 90-degree intervals in the direction along the circumference of the roller-shaped charging member and at both ends of the discharging region, and the average of a total of eight points is calculated.

Thickness of the Surface Layer

The thickness of the surface layer may be 3 µm or more and 25 µm or less, preferably 5 µm or more and 20 µm or less, more preferably 6 µm or more and 15 µm or less.
The thickness of the surface layer is measured by cutting the surface layer in the thickness direction and observing the resulting cross-section using an optical microscope. Resistance Z of the Conductive Member
For the conductive member according to this exemplary embodiment, the resistance Z as measured by the impedance method may be 4.5 × 10⁵ Q or less, preferably 4.0 × 10⁵ Q or less, more preferably 3.5 × 10⁵ S2 or less. The resistance Z, furthermore, may be 1.0 × 10⁴ Q or more, preferably 5.0 × 10⁴ S2 or more.
When the resistance Z as measured by the impedance method is adjusted to fall within these ranges, the permeability of the entire conductive member to electric current improves. The occurrence of color streaks in the axial direction, therefore, is further reduced during image formation.
The procedure for measuring the resistance Z is as follows.
As the power supply and ammeter, SI 1260 impedance/gain phase analyzer (manufactured by TOYO Corporation) is used, and as the current amplifier, 1296 dielectric interface (manufactured by TOYO Corporation) is used.
With the substrate in the samples for impedance measurement (conductive members) as the cathode and the surface of the conductive members with a 1.5-cm wide aluminum plate wound therearound as the anode, an AC voltage of 1 Vp-p is applied within the frequency range of 1 MHz to 1 mHz, starting from higher frequencies, and the resistance Z of each sample by the AC impedance method is measured.

Method for Manufacturing the Conductive Member

An example of a method for manufacturing the conductive member according to this exemplary embodiment will be described below.
A roller-shaped member composed of a cylindrical or columnar substrate and an elastic layer provided on the outer circumferential surface of the substrate is prepared. The method for producing this roller-shaped member is not particularly limited. An example is the production method of wrapping a mixture containing a rubber material, optionally with a conductive agent and other additives, around the substrate and forming an elastic layer by vulcanizing the rubber through heating.
The method for providing the surface layer on the outer circumferential surface of the elastic layer is not particularly limited; however, it may be provided by applying a dispersion obtained by dissolving and dispersing the first resin, second resin, and conductive agent in a solvent to the outer circumferential surface of the elastic layer and drying the applied dispersion. Examples of methods for applying the dispersion include blade coating, wire bar coating, spray coating, dip coating, bead coating, air knife coating, and curtain coating.
By setting the dew point of the environment during the step of applying the dispersion to the outer circumferential surface of the elastic layer and drying the applied dispersion to 12°C or above and 18°C or below, furthermore, the conductive member according to this exemplary embodiment is obtained easily. It should be noted that usually, the dew point of the environment during the step of drying the applied dispersion is approximately 5°C.
In addition, by halving the velocity of air during the drying, for example, in the step of drying the applied dispersion, the conductive member according to this exemplary embodiment is obtained easily.

Applications of the Conductive Member

The conductive member according to this exemplary embodiment is used in, for example, a charging roller for charging the surface of an image carrier in apparatuses such as electrophotographic copiers or electrostatic printers, a transfer roller for transferring a toner image formed on the image carrier to a transfer medium, a toner transport roller for transporting toner onto the image carrier, a conductive roller used in combination with a conductive belt for electrostatic transport of paper to feed power to or drive the belt, or a cleaning roller for removing toner on the image carrier. In inkjet image forming apparatuses, furthermore, the conductive member is used in, for example, a feed roller for charging an intermediate transfer body before the ink is ejected from the inkjet head onto it.
The conductive member according to this exemplary embodiment is suitable for use as a charging roller in particular.
The form of a conductive member 121A that is a roller-shaped member has been described as a conductive member according to this exemplary embodiment in the foregoing, but the conductive member according to this exemplary embodiment is not limited to it; it may be an endless belt-shaped member or a sheet-shaped member.
The conductive member according to this exemplary embodiment, furthermore, may be in a configuration in which it includes, for example, an adhesive layer (primer layer) disposed between the substrate and the elastic layer, a resistance adjustment layer or migration prevention layer disposed between the elastic layer and the surface layer, and a coating layer (protective layer) disposed outside the surface layer (on the outermost surface).

Charging Device, Image Forming Apparatus, and Process Cartridge

A charging device according to an exemplary embodiment includes a conductive member according to the above exemplary embodiment.
The charging device according to this exemplary embodiment may be a charging device that includes a conductive member according to the above exemplary embodiment and charges an image carrier through contact electrification.
The width of contact of the conductive member with the image carrier in the circumferential direction (i.e., the width of the conductive member in the circumferential direction in the region in which the image carrier and the conductive member are in contact with each other) is not particularly limited; for example, it may fall within the range of 0.5 mm to 5 mm, preferably the range of 1 mm to 3 mm.
A process cartridge according to an exemplary embodiment is attachable to and detachable from, for example, an image forming apparatus configured as described below and includes a charging device that charges the surface of the image carrier. As the charging device, furthermore, a charging device according to the above exemplary embodiment is used.
The process cartridge according to this exemplary embodiment may optionally include, for example, at least one selected from the group consisting of an image carrier, an electrostatic latent image forming device that forms an electrostatic latent image on a charged surface of the image carrier, a developing device that develops, using toner, the latent image on the surface of the image carrier to form a toner image, a transfer device that transfers the toner image formed on the surface of the image carrier to a recording medium, and a cleaning device that cleans the surface of the image carrier.
An image forming apparatus according to an exemplary embodiment includes an image carrier, a charging device that charges the surface of the image carrier, an electrostatic latent image forming device that forms an electrostatic latent image on the charged surface of the image carrier, a developing device that develops, using a developer containing toner, the electrostatic latent image on the surface of the image carrier to form a toner image, and a transfer device that transfers the toner image to the surface of a recording medium. As the charging device, furthermore, a charging device according to the above exemplary embodiment is used.
An image forming apparatus and a process cartridge according to exemplary embodiments will now be described with reference to drawings.
Fig. 3 is a schematic view illustrating the structure of an image forming apparatus according to an exemplary embodiment. It should be noted that the arrow UP presented in the drawing indicates the vertically upward direction.
The image forming apparatus 210 includes, as illustrated in Fig. 3, an image forming apparatus body 211, inside which the individual components are housed. Inside the image forming apparatus body 211, there are a container section 212, in which a recording medium P, such as paper, is stored, an image forming section 214, which forms an image on the recording medium P, a transport section 216, which transports the recording medium P from the container section 212 to the image forming section 214, and a controller 220, which controls the operation each section of the image forming apparatus 210. In an upper portion of the image forming apparatus body 211, furthermore, there is an ejection section 218, to which the recording medium P with the image formed thereon by the image forming section 214 is ejected.
The image forming section 214 includes image forming units 222Y, 222M, 222C, and 222K that form toner images in the colors of yellow (Y), magenta (M), cyan (C), and black (K), respectively (hereinafter the image forming units 222Y to 222K), an intermediate transfer belt 224 (an example of a transfer medium) to which the toner images formed at the image forming units 222Y to 222K are transferred, first transfer rollers 226 (an example of transfer rollers) that transfer the toner images formed at the image forming units 222Y to 222K to the intermediate transfer belt 224, and a second transfer roller 228 (an example of a transfer member) that transfers the toner images on the intermediate transfer belt 224, transferred there by the first transfer rollers 226, from the intermediate transfer belt 224 to the recording medium P. It should be noted that the image forming section 214 is not limited to this configuration; it may be in other configurations and only needs to be one that forms an image on the recording medium P (an example of a transfer substrate).
In the illustrated example, the unit formed by the intermediate transfer belt 224, first transfer rollers 226, and second transfer roller 228 corresponds to an example of a transfer device. It should be noted that this unit may be configured as a cartridge (process cartridge).
The image forming units 222Y to 222K are arranged in a row in the middle of the image forming apparatus 210 in the vertical direction, inclined with respect to the horizontal direction. The image forming units 222Y to 222K, furthermore, each have a photoreceptor 232 (an example of an image carrier) that rotates in one direction (e.g., clockwise in Fig. 3). It should be noted that the image forming units 222Y to 222K are configured in the same manner; in Fig. 3, therefore, the components of the image forming units 222M, 222C, and 222K are illustrated without reference signs.
Around each photoreceptor 232, there are a charging device 223 having a charging roller 223A (an example of a charging member) with which it charges the photoreceptor 232, an exposure device 236 (an example of an electrostatic latent image forming device) that exposes the photoreceptor 232 charged by the charging device 223 to light to form an electrostatic latent image on the photoreceptor 232, a developing device 238 that develops the latent image formed on the photoreceptor 232 by the exposure device 236 to form a toner image, and a removing member (e.g., a cleaning blade) 240 that removes residual toner on the photoreceptor 232 by making contact with the photoreceptor 232, in this order from upstream in the direction of rotation of the photoreceptor 232.
In the illustrated example, the photoreceptor 232, charging device 223, exposure device 236, developing device 238, and removing member 240 are held together in a housing 222A, forming a cartridge (process cartridge).
As the exposure device 236, a self-scanning LED printhead is used. Alternatively, the exposure device 236 may be an optical exposure device that directs light from a light source onto the photoreceptor 232 via a polygon mirror.
The exposure device 236 is configured to form a latent image based on an image signal transmitted from the controller 220. An example of an image signal transmitted from the controller 220 is an image signal that the controller 220 acquires from an external device.
The developing device 238 includes a developer feeder 238A that supplies the developer to the photoreceptor 232 and multiple transport members 238B that transport the developer to be attached to the developer feeder 238A while stirring it.
The intermediate transfer belt 224 is shaped like a ring and also is positioned above the image forming units 222Y to 222K. Inside the intermediate transfer belt 224, there are wrapping rollers 242 and 244 around which the intermediate transfer belt 224 is wrapped. The intermediate transfer belt 224 is configured to circulate (rotate) in one direction (e.g., counterclockwise in Fig. 3) while in contact with the photoreceptors 232 as a result of the rotation of any of the wrapping rollers 242 and 244. It should be noted that the wrapping roller 242 is configured as a "facing roller," a roller that faces the second transfer roller 228.
The first transfer rollers 226 face the photoreceptors 232 with the intermediate transfer belt 224 interposed therebetween. The points between the first transfer rollers 226 and the photoreceptors 232 are designated as first transfer points, at which the toner images formed on the photoreceptors 232 are transferred to the intermediate transfer belt 224.
The second transfer roller 228 faces the wrapping roller 242 with the intermediate transfer belt 224 interposed therebetween. The point between the second transfer roller 228 and the wrapping roller 242 is designated as a second transfer point, at which the toner images transferred to the intermediate transfer belt 224 are transferred to the recording medium P.
In the transport section 216, there are a pickup roller 246 that retrieves and sends out the recording medium P stored in the container section 212, a transport path 248 along which the recording medium P sent out by the pickup roller 246 is transported, and multiple transport rollers 250 that are positioned along the transport path 248 and transport the recording medium P sent out by the pickup roller 246 to the second transfer point.
Downstream of the second transfer point in the direction of transport, there is a fixing device 260 that fixes the toner image formed on the recording medium P by the image forming section 214 onto the recording medium P.
The fixing device 260 includes a heating roller 264 that heats the image on the recording medium P and a pressure roller 266 as an example of a pressurizing member. Inside the heating roller 264, there is a heat source 264B.
Downstream of the fixing device 260 in the direction of transport, there are ejection rollers 252 that eject the recording medium P with the fixed toner image thereon to the ejection section 218.
The image forming operations, through which an image is formed on a recording medium P, in the image forming apparatus 210 will now be described.
In the image forming apparatus 210, a recording medium P retrieved and sent out from the container section 212 by the pickup roller 246 is delivered to the second transfer point by the multiple transport rollers 250.
Meanwhile, at the image forming units 222Y to 222K, the photoreceptor 232 charged by the charging device 223 is exposed to light by the exposure device 236, resulting in the formation of a latent image on the photoreceptor 232. This latent image is developed by the developing device 238, through which a toner image is formed on the photoreceptor 232. The toner images in their respective colors formed at the image forming units 222Y to 222K are layered on the intermediate transfer belt 224 at the first transfer points, and thereby a color image is formed. Then the color image formed on the intermediate transfer belt 224 is transferred to the recording medium P at the second transfer point.
The recording medium P with the transferred toner images thereon is transported to the fixing device 260, and the transferred toner images are fixed by the fixing device 260. The recording medium P with the fixed toner images thereon is ejected to the ejection section 218 by the ejection rollers 252. In such a manner, a series of image forming operations is performed.
It should be noted that the image forming apparatus 210 according to this exemplary embodiment is not limited to the above configuration; a known image forming apparatus may be employed, such as a direct-transfer image forming apparatus, which forms a toner image on each of photoreceptors 232 in image forming units 222Y to 222K and transfers the toner images directly to a recording medium P.

Examples

Examples will now be described, but none of the above exemplary embodiments is limited to these examples. In the following description, "parts" and "%" are all by mass unless stated otherwise.

Example 1: Fabrication of a Conductive Member

Formation of an Elastic Layer

A mixture prepared by adding 15 parts by mass of a conductive agent (carbon black; Asahi Thermal, manufactured by Asahi Carbon, Co., Ltd.), 1 part by mass of a vulcanizing agent (sulfur, 200 mesh. Manufactured by Tsurumi Chemical Industry Co., Ltd.) as an extra additive blended into the elastic layer, and 2.0 parts by mass of a vulcanization accelerator (NOCCELER DM, manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) as an extra additive blended into the elastic layer to 100 parts by mass of an elastic material (epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber) is kneaded using an open-roll mill to give a composition for elastic layer formation. Using a press molding machine, the composition for elastic layer formation is wrapped around the outer circumferential surface of an 8-mm diameter shaft made of SUS303 (a substrate), with an adhesive layer interposed therebetween; the resulting workpiece is placed in a furnace at a temperature of 180°C and subjected to heat treatment for 30 minutes, through which a 3.5-mm thick elastic layer is formed on the shaft. The outer circumferential surface of this elastic layer is polished, yielding a 14-mm diameter conductive elastic roller having a 3.0-mm thick elastic layer.

Formation of a Surface Layer

Fifteen parts by mass of a composition composed of 76 parts by mass of a polyamide resin (N-methoxymethylated nylon; F30K, manufactured by Nagase ChemteX Corporation) as a first resin, 24 parts by mass of a polyvinyl butyral resin (S-LEC BL-1, manufactured by Sekisui Chemical Co., Ltd.) as a second resin, 13 parts by mass of carbon black (MONARCH 1000, manufactured by Cabot Corporation) as a conductive agent, 10 parts by mass of a porous polyamide filler (Orgasol 2001 UD NAT 1, manufactured by Arkema) as a filler, 1.0 part by mass of an acid catalyst (NACURE 4167, manufactured by King Industries, Inc.), and 0.025 parts by mass of a leveling agent (polyether-modified polydimethylsiloxane as a polyether-modified polysiloxane; BYK 307, manufactured by BYK-Chemie GmbH) is diluted with 85 parts by mass of methanol and dispersed in a bead mill to give a dispersion. In an environment with a temperature of 24°C and a dew point of 14°C, the resulting dispersion is applied to the outer circumferential surface of the elastic layer of the conductive elastic roller by dip coating and dried by air drying, and then crosslinking is induced by heating at 140°C for 30 minutes, through which a 10-µm thick surface layer is formed; in this manner, a conductive member is obtained.

Comparative Example 1

A conductive member is obtained in the same manner as in Example 1, except that the dew point is set to 5°C during the air drying in the formation of the surface layer.

Examples 2 to 8

A conductive member is obtained in the same manner as in Example 1, except that the coating environment (dew point) and the amounts of the first and second resins added are changed as in Table 1.

Example 9

A conductive member is obtained in the same manner as in Example 1, except that the airflow inside the coating booth is halved during the air drying in the formation of the surface layer.

Example 10

A conductive member is obtained in the same manner as in Example 1, except that the airflow inside the coating booth is further reduced during the air drying in the formation of the surface layer.
The following characteristics of the conductive member obtained in each example or comparative example are measured according to the methods already described herein. The results obtained are presented in Table 2.

Measurement of Conductive Points by Conductive Atomic Force Microscopy (C-AFM)

On the surface of the conductive member obtained, conductive points are measured under the conditions specified below using AFM5200S (AFM/Current), manufactured by Hitachi High-Tech Corporation, and a CL scanner (110 µm) for S-image. Portions with 60 pA or more are defined as conductive portions, and the percentage area and average area of conductive portions measured in the shape of particles are calculated. The measurement results are presented in Table 2.

On the surface of the conductive member obtained, 50-µm square (= 50 µm × 50 µm) areas are each divided into a grid of 256 × 256 segments, and the value of current flowing in each segment is measured using the aforementioned conductive atomic force microscope while a 100-nm diameter probe (cantilever) is moved with -30 V applied to it.
The percentage area of segments with a current value of 60 pA or more to all segments is presented in Table 2.

Measurement of the Resistance Z of the Conductive Member

As the power supply and ammeter, SI 1260 impedance/gain phase analyzer (manufactured by TOYO Corporation) is used, and as the current amplifier, 1296 dielectric interface (manufactured by TOYO Corporation) is used.
With the substrate in the samples for impedance measurement (conductive members) as the cathode and the surface of the conductive members with a 1.5-cm wide aluminum plate wound therearound as the anode, an AC voltage of 1 Vp-p is applied within the frequency range of 1 MHz to 1 mHz, starting from higher frequencies, and the resistance Z of each sample by the AC impedance method is measured.

Evaluations

Color Streak Evaluation

The conductive member obtained in the Example or Comparative Example is installed as a charging roller into a modified version of an image forming apparatus (DocuCentre-V C7776, manufactured by FUJIFILM Business Innovation Corp.), and an A4 image with an area coverage of 30% is produced on 5,000 sheets under the conditions of 28°C and 85% RH.
Based on the level of color streaks extending in the direction along the axis of the photoreceptor on the image produced on the 5000th sheet, an evaluation is made on a scale of GO to G3. GO to G2 indicate levels acceptable in practical use. The evaluation results are presented in Table 2.

G0: The occurrence of color streaks extending in the direction along the axis of the photoreceptor is not observed.
G0.5: The number of color streaks extending in the direction along the axis of the photoreceptor is 1 or fewer.
G1: The number of color streaks extending in the direction along the axis of the photoreceptor is 2 or more and 4 or fewer.
G1.5: The number of color streaks extending in the direction along the axis of the photoreceptor is 5 or more and 7 or fewer.
G2: The number of color streaks extending in the direction along the axis of the photoreceptor is 8 or more and 10 or fewer.
G2.5: The number of color streaks extending in the direction along the axis of the photoreceptor is 11 or more and 13 or fewer.
G3: The number of color streaks extending in the direction along the axis of the photoreceptor is 14 or more.

Mechanical Strength Evaluation

The evaluation of the mechanical strength of the surface layer is performed through an MIT test.
The MIT test is as specified in JIS P 8115: 2001 (MIT method).
Specifically, a strip-shaped test specimen having a width of 15 mm in the circumferential direction and a length of 200 mm (the thickness of the test specimen is the thickness of the surface layer) is cut out from the surface layer of the conductive member.
With both ends held and a tension of 1 kgf applied, this strip-shaped test specimen is repeatedly bent (folded) in the 90° directions to the left and right, supported by a clamp having a radius of curvature R = 0.05. The number of bends during this process until the strip-shaped test specimen breaks is defined as the fold number, and strength is evaluated based on the fold number according to the evaluation criteria below.
It should be noted that the MIT test is performed in an environment with a temperature of 22°C and a humidity of 55% RH.
The evaluation results are presented in Table 2.

G0: The fold number is 100,000 or more.
G1: The fold number is 50,000 or more and less than 100,000.
G2: The fold number is 10,000 or more and less than 50,000.
G3: The fold number is less than 10,000.

Table 1

	Surface layer formation environment		First resin		Second resin		Conductive agent		Filler		Acid catalyst		Silicon-containing compound
	Dew point (°C)	Air velocity (m/sec)	Type	Amount added (parts)	Type	Amount added (parts)	Type	Amount added (parts)	Type	Amount added (parts)	Type	Amount added (parts)	Type	Amount added (parts)
Example 1	14	1.4	PA1	76	PVB1	24	CB1	13	F1	10	CAT1	1	LA1	0.025
Comparative Example 1	5	1.4	PA1	76	PVB1	24	CB1	13	F1	10	CAT1	1	LA1	0.025
Example 2	14	1.4	PA1	90	PVB1	10	CB1	13	F1	10	CAT1	1	LA1	0.025
Example 3	20	1.4	PA1	76	PVB1	24	CB1	13	F1	10	CAT1	1	LA1	0.025
Example 4	15	1.4	PA1	76	PVB1	24	CB1	13	F1	10	CAT1	1	LA1	0.025
Example 5	16	1.4	PA1	76	PVB1	24	CB1	13	F1	10	CAT1	1	LA1	0.025
Example 6	14	1.4	PA1	60	PVB1	40	CB1	13	F1	10	CAT1	1	LA1	0.025
Example 7	14	1.4	PA1	70	PVB1	30	CB1	13	F1	10	CAT1	1	LA1	0.025
Example 8	14	1.4	PA1	65	PVB1	35	CB1	13	F1	10	CAT1	1	LA1	0.025
Example 9	14	0.7	PA1	76	PVB1	24	CB1	13	F1	10	CAT1	1	LA1	0.025
Example 10	14	0.4	PA1	76	PVB1	24	CB1	13	F1	10	CAT1	1	LA1	0.025

Table 2

	Surface layer								Conductive member	Evaluations
	First resin	Second resin		Conductive agent	Silicon-containing compound	Conductive point measurement		Percentage (% by area) of regions with a current value of 60 pA or more	Resistance Z (Ω)	Color streaks	Mechanical strength
	Type	Type	Amount (parts by mass) in relation to the total of the first and second resins	Type	Amount contained (parts by mass)	Percentage area (% by area) of particulate conductive portions	Average area (µm²) of particulate conductive portions		Resistance Z (Ω)	Color streaks	Mechanical strength
Example 1	PA1	PVB1	24	CB1	0.025	16	0.08	60	3.5×10⁵	G1.5	G0
Comparative Example 1	PA1	PVB1	24	CB1	0.025	10	0.05	40	1.5×10⁶	G3	G0
Example 2	PA1	PVB1	10	CB1	0.025	15	0.03	35	1.3×10⁶	G2	G0
Example 3	PA1	PVB1	24	CB1	0.025	85	0.5	75	2.1×10⁵	G0	G1
Example 4	PA1	PVB1	24	CB1	0.025	35	0.22	63	5.5×10⁵	G1	G0
Example 5	PA1	PVB1	24	CB1	0.025	65	0.43	72	2.3×10⁵	G0	G1
Example 6	PA1	PVB1	40	CB1	0.025	32	1.2	82	3.0×10^s	G0.5	G1
Example 7	PA1	PVB1	30	CB1	0.025	25	0.15	61	6.5×10⁵	G1.5	G0
Example 8	PA1	PVB1	35	CB1	0.025	30	0.55	75	6.0×10⁵	G1	G1
Example 9	PA1	PVB1	24	CB1	0.025	41	0.35	65	2.8×10⁵	G0.5	G0
Example 10	PA1	PVB1	24	CB1	0.025	45	0.38	70	2.5×10⁵	G0	G0

The definitions of the abbreviations in Tables 1 and 2 are as follows.

First Resin
- PA1: Polyamide resin (F30K, manufactured by Nagase ChemteX Corporation)
Second Resin
- PVB1: Polyvinyl butyral resin (S-LEC BM-1, manufactured by Sekisui Chemical Co., Ltd.)
Conductive Agent
- CB1: Carbon black (MONARCH 1000, manufactured by Cabot Corporation) Filler
- F1: Porous polyamide filler (Orgasol 2001 UD NAT 1, manufactured by Arkema) Acid Catalyst
- CAT1: Amine-neutralized phosphoric acid catalyst (NACURE 4167, manufactured by King Industries, Inc.)
Silicon-Containing Compound
LA1: Polyether-modified polydimethylsiloxane as a polyether-modified polysiloxane (BYK 307, manufactured by BYK-Chemie GmbH)

From these results, it can be understood that the conductive members in the Examples are superior in the reduction of the occurrence of color streaks compared with the conductive member in the Comparative Example.
The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.

Appendix

(((1))) A conductive member, wherein a percentage area of particulate conductive portions measured when conductive points on a surface are measured by conductive atomic force microscopy is 15% by area or more.
(((2))) A conductive member, wherein an average area of particulate conductive portions measured when conductive points on a surface are measured by conductive atomic force microscopy is 0.05 µm² or more.
(((3))) The conductive member according to (((1))), wherein the percentage area of the conductive portions is 15% by area or more and 80% by area or less.
(((4))) The conductive member according to (((3))), wherein the percentage area of the conductive portions is 30% by area or more and 60% by area or less.
(((5))) The conductive member according to (((1))) or (((2))), wherein the average area of the conductive portions is 0.05 µm² or more and 1.0 µm² or less.
(((6))) The conductive member according to (((5))), wherein the average area of the conductive portions is 0.20 µm² or more and 0.50 µm² or less.
(((7))) The conductive member according to any one of (((1))) to (((6))), wherein when a current value is measured on the surface while a 100-nm diameter probe is moved with -30 V applied thereto, 50-µm square regions in which a value of current flowing per segment is 60 pA or more, where the regions are each divided into a grid of 256 × 256 segments, constitute 60% by area or more.
(((8))) The conductive member according to any one of (((1))) to (((7))), wherein the conductive member includes a substrate, an elastic layer provided on the substrate, and a surface layer provided on the elastic layer.
(((9))) The conductive member according to (((8))), wherein the surface layer contains at least one first resin, at lease one second resin, and at least one conductive agent.
(((10))) The conductive member according to (((9))), wherein the surface layer has a sea-island structure composed of a sea portion containing the first resin and island portions containing the second resin.
(((11))) A charging device including the conductive member according to any one of (((1))) to (((10))).
(((12))) A process cartridge attachable to and detachable from an image forming apparatus, the process cartridge including the charging device according to (((11))).
(((13))) An image forming apparatus including an image carrier; the charging device according to (((11))) that charges a surface of the image carrier; an electrostatic latent image forming device that forms an electrostatic latent image on the charged surface of the image carrier; a developing device that develops, using a developer containing toner, the electrostatic latent image on the surface of the image carrier to form a toner image; and a transfer device that transfers the toner image to a surface of a recording medium.

According to (((1))) or (((8))) of the present disclosure, there is provided a conductive member superior in the reduction of the occurrence of color streaks compared with when the percentage area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is less than 15% by area.
According to (((2))) of the present disclosure, there is provided a conductive member superior in the reduction of the occurrence of color streaks compared with when the average area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is less than 0.05 µm².
According to (((3))) of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than when the percentage area of the conductive portions is less than 15% by area or exceeds 80% by area.
According to (((4))) of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than when the percentage area of the conductive portions is less than 30% by area or exceeds 60% by area.
According to (((5))) of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than when the average area of the conductive portions is less than 0.05 µm² or exceeds 1.0 µm².
According to (((6))) of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than when the average area of the conductive portions is less than 0.20 µm² or exceeds 0.50 µm².
According to (((7))) of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than in the case in which when the current value is measured on the surface while a 100-nm diameter probe is moved with -30 V applied to it, 50-µm square regions in which the value of current flowing per segment is 60 pA or more, where the regions are each divided into a grid of 256 × 256 segments, constitute less than 60% by area.
According to (((9))) or (((10))) of the present disclosure, there is provided a conductive member better in the reduction of the occurrence of color streaks than when the surface layer contains only one type of resin.
According to (((11))), (((12))), or (((13))) of the present disclosure, there is provided a charging device, process cartridge, or image forming apparatus superior in the reduction of the occurrence of color streaks compared with when the conductive member included is one for which the percentage area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is less than 15% by area or the average area of particulate conductive portions measured when conductive points on the surface are measured by conductive atomic force microscopy is less than 0.05 µm².

Claims

A conductive member, wherein:
a percentage area of particulate conductive portions measured when conductive points on a surface are measured by conductive atomic force microscopy is 15% by area or more.
A conductive member, wherein:
an average area of particulate conductive portions measured when conductive points on a surface are measured by conductive atomic force microscopy is 0.05 µm² or more.
The conductive member according to claim 1, wherein:
the percentage area of the conductive portions is 15% by area or more and 80% by area or less.
The conductive member according to claim 3, wherein:
the percentage area of the conductive portions is 30% by area or more and 60% by area or less.
The conductive member according to claim 1 or 2, wherein:
the average area of the conductive portions is 0.05 µm² or more and 1.0 µm² or less.
The conductive member according to claim 5, wherein:
the average area of the conductive portions is 0.20 µm² or more and 0.50 µm² or less.
The conductive member according to any one of claims 1 to 6, wherein:
when a current value is measured on the surface while a 100-nm diameter probe is moved with -30 V applied thereto, 50-µm square regions in which a value of current flowing per segment is 60 pA or more, where the regions are each divided into a grid of 256 × 256 segments, constitute 60% by area or more.
The conductive member according to any one of claims 1 to 7, wherein:
the conductive member includes a substrate, an elastic layer provided on the substrate, and a surface layer provided on the elastic layer.
The conductive member according to claim 8, wherein:
the surface layer contains at least one first resin, at lease one second resin, and at least one conductive agent.
The conductive member according to claim 9, wherein:
the surface layer has a sea-island structure composed of a sea portion containing the first resin and island portions containing the second resin.
A charging device comprising:
the conductive member according to any one of claims 1 to 10.
A process cartridge attachable to and detachable from an image forming apparatus, the process cartridge comprising:
the charging device according to claim 11.
An image forming apparatus comprising:
an image carrier;

the charging device according to claim 11 that charges a surface of the image carrier;

an electrostatic latent image forming device that forms an electrostatic latent image on the charged surface of the image carrier;

a developing device that develops, using a developer containing toner, the electrostatic latent image on the surface of the image carrier to form a toner image; and

a transfer device that transfers the toner image to a surface of a recording medium.