JP7429170B2 - developing roller - Google Patents

Description

The present invention relates to a developing roller.

The developing roller used in image forming devices such as copying machines, printers, and facsimile machines that use electrophotography has the function of applying a uniform frictional charge to toner and stably transporting a predetermined amount of toner to the developing area. has. In recent years, toner characteristics have been improved in response to higher speeds, longer lifespans, and higher image quality in electrophotographic devices. Improving the developer transportability of rollers is also being considered.

A developing roller used in an electrophotographic image forming apparatus generally includes an elastic layer and a covering layer on the outer periphery of a shaft body. As the material for the coating layer, for example, a material whose main component is a paint binder such as polycarbonate-based, ether-based, or polyester-based polyurethane resin is used. It is widely known that conductive carbon black is dispersed in the material of the coating layer in order to impart conductivity (see Patent Documents 1 and 2).

Japanese Patent Application Publication No. 2003-3032 Japanese Patent Application Publication No. 2002-363426

In recent years, efforts have been made to reduce the melting point of toner used in electrophotographic copying machines with the aim of reducing power consumption and achieving high-speed printing. However, such a low-melting-point toner is easily melted by frictional heat caused by the pressure of a developing roller or other regulating member, and in a high-humidity environment, the toner itself tends to lose its chargeability due to the influence of moisture. Therefore, under a high temperature and high humidity environment, a phenomenon called filming occurs in which the toner melts and sticks to the developing roller. When filming occurs, the charging performance of the developing roller decreases, causing a decrease in the charging performance of the toner, resulting in problems such as image defects such as fogging and roughness. Therefore, in order to suppress toner sticking, it is necessary to provide the surface of the developing roller with toner releasability.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a developing roller that has good toner releasability and excellent filming resistance.

The present invention provides a developing roller comprising a shaft body, an elastic layer provided on the outer surface of the shaft body, and a covering layer provided outside the elastic layer, the developing roller having an adhesion force determined by a nanoindentation method of the covering layer. is 4.0 μN or less.

The capacitance of the coating layer is preferably 11 nF or less at 0.1 Hz.

The MD-1 hardness of the coating layer is preferably 30° or more and 60° or less.

The hexadecane contact angle on the surface of the developing roller is preferably 30° or more.

The coating layer preferably contains a silicone-modified urethane resin, and the resistance value of the surface of the developing roller is preferably 1×10 ⁷ Ω or more and 9×10 ⁹ Ω or less.

According to the present invention, it is possible to provide a developing roller that has good toner releasability and excellent filming resistance.

FIG. 1 is a perspective view showing an embodiment of a developing roller of the present invention. FIG. 2 is a schematic front view showing a device for measuring resistance on the surface of a developing roller. 1 is a graph showing typical loading and unloading curves determined by a nanoindenter.

Embodiments of the present invention will be described in detail below with reference to the drawings.
[Developing roller]
As shown in FIG. 1, the developing roller 1 of the present invention includes a shaft 2, an elastic layer 3 provided on the outer surface of the shaft 2, and a coating layer 4 provided outside the elastic layer 3.
The details of each configuration will be explained below.

<Shaft body>
As the shaft body 2, preferably, a shaft body having conductive properties and used in a conventionally known developing roller can be used. The shaft body 2 is preferably made of at least one metal selected from the group consisting of iron, aluminum, stainless steel, and brass, for example. Incidentally, such a shaft body 2 is also generally known by the name "core bar".

The shaft body 2 may include an insulating resin. The insulating resin may be, for example, a thermoplastic resin or a thermosetting resin. The shaft body 2 may include, for example, a core body made of insulating resin and a plating layer provided on the core body. Such a shaft body 2 can be obtained, for example, by plating a core body made of an insulating resin to make it conductive.
The shaft body 2 is preferably a metal core in order to obtain good conductive properties.

The shape of the shaft body 2 is preferably, for example, rod-like or tubular. The cross-sectional shape of the shaft body 2 may be, for example, circular, elliptical, or non-circular such as a polygon. The outer peripheral surface of the shaft body 2 may be subjected to treatments such as cleaning treatment, degreasing treatment, and primer treatment.

The length of the shaft body 2 in the axial direction is not particularly limited, and may be adjusted as appropriate depending on the form of the image forming apparatus installed. Further, the diameter of the shaft body 2 (the diameter of the circumscribed circle) is not particularly limited, and may be adjusted as appropriate depending on the form of the image forming apparatus installed.

<Elastic layer>
The elastic layer 3 has a hardness and elasticity that allows it to be pressed against the photoreceptor with an appropriate nip width and nip pressure so that toner can be supplied to the electrostatic latent image formed on the surface of the photoreceptor in just the right amount. It is provided to apply it to the roller 1. Elastic layer 3 contains silicone rubber. Silicone rubber has the advantage of low compressive stress distortion caused by pressing. Examples of the silicone rubber include polydimethylsiloxane, polymethyltrifluoropropylsiloxane, polymethylvinylsiloxane, polyphenylvinylsiloxane, and copolymers of these siloxanes.

By incorporating a conductivity imparting agent such as an electronically conductive substance or an ionically conductive substance into the elastic layer 3, its conductivity can be adjusted as appropriate. Examples of electronically conductive substances include conductive carbon such as Ketjenblack EC and acetylene black, rubber carbon such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, and MT, and oxidized color (ink). Examples include metals such as carbon, copper, silver, and germanium, and metal oxides thereof. Among these, carbon black (conductive carbon, carbon for rubber, carbon for color (ink)) is preferable because it is easy to control conductivity with a small amount. Examples of ion conductive substances include inorganic ion conductive substances such as sodium perchlorate, lithium perchlorate, calcium perchlorate, lithium chloride, lithium bisimide, potassium bisimide, modified aliphatic dimethylammonium ethosulfate, Examples include organic ionically conductive substances such as stearyl ammonium acetate. A reactive ether-modified silicone oil may be added to the elastic layer 3.

<Coating layer>
The base resin of the coating layer 4 is preferably a silicone-modified urethane resin. The coating layer 4 can be formed by heating and curing a coating layer composition containing (A) a silicone-modified polyol, (B) an isocyanate compound, and (C) a roughening agent. Note that the coating layer 4 contains a base resin and a roughening agent, but preferably does not contain a conductivity imparting agent.
The details of the coating layer composition will be explained below.

(A) Silicone-modified polyol A silicone-modified polyol is a prepolymer obtained by polymerizing a composition consisting of a modified silicone oil and an isocyanate compound.
Details of the modified silicone oil and isocyanate compound used in the synthesis of the silicone-modified polyol will be explained below. Modified silicone oils include silicone oils modified at both ends and silicone oils modified at one end.

-Both ends modified silicone oil-
The double-end modified silicone oil is a type of so-called reactive silicone oil, and has the property of polymerizing with isocyanate compounds. Therefore, it is preferable that both terminally modified silicone oil has both terminals of the silicone chain modified with an ether group, an amino group (primary or secondary amino group), a mercapto group, or a hydroxyl group. These silicone oils modified at both ends include ether-modified silicone oil at both ends, amino-modified silicone oil at both ends, mercapto-modified silicone oil at both ends, carboxyl-modified silicone oil at both ends, phenol-modified silicone oil at both ends, carbinol-modified silicone at both ends. It is commercially available as an oil.

Here, as a preferable both-terminally modified silicone oil used in the present invention, a both-terminally modified silicone oil represented by the following general formula (1) can be mentioned.

In general formula (1), R represents -C ₃ H ₆ OC ₂ H ₄ OH or -C ₃ H ₆ OCH ₂ -C(CH ₂ OH) ₂ C ₂ H ₅ , and n is 20 or less. Represents an integer.

Among the silicone oils modified at both ends represented by the general formula (1), it is particularly preferable to use a silicone oil in which R at both ends is -C ₃ H ₆ OC ₂ H ₄ OH and n is about 10. . Commercially available silicone oils can be obtained as appropriate.

In addition, in the general formula (1), the functional group bonded to the silicon atom is a methyl group, but a silicone oil modified at both ends in which the methyl group is substituted with a hydrogen atom may be used.

By containing the silicone oil modified at both ends in the composition for forming the coating layer 4, it is possible to impart appropriate elasticity to the coating layer 4, and the electrical characteristics of the coating layer 4 can be adjusted. , the occurrence of filming can be effectively suppressed.

-Silicone oil modified with diol at one end-
Silicone oil modified with a diol at one end is a reactive silicone oil like the silicone oil modified at both ends, but has two hydroxyl groups bonded to one end of the silicone chain. Normally, when a silicone oil modified at both ends and an isocyanate compound are polymerized, a linear polyurethane is produced, but by using a silicone oil modified at one end with a diol, a branched chain is introduced into the polyurethane, and the developing roller 1 It is possible to improve the fine roughness at the nano level.

Examples of the silicone oil modified with a diol at one end include silicone oil modified at one end represented by the following general formula (2).

In general formula (2), R' represents -C ₃ H ₆ OCH ₂ -C(CH ₂ OH) ₂ C ₂ H ₅ , and n represents an integer of 20 or less.

Among the silicone oils modified with diol at one end represented by the general formula (2), it is particularly preferable to use silicone oils in which n is about 10. In general formula (2), the functional group bonded to the silicon atom is a methyl group, but a silicone oil in which this methyl group is substituted with a hydrogen atom may also be used.

In the present invention, the one-end diol-modified silicone oil used for preparing the silicone-modified polyol is preferably 1 part by mass or more and 10 parts by mass or less, and 2 parts by mass or more, with respect to 100 parts by mass of the both-terminally modified silicone oil. More preferably, the amount is 8 parts by mass or more and 8 parts by mass or less. By adjusting the amount of diol-modified silicone oil at one end to the silicone oil modified at both ends within the above range, the surface roughness of the coating layer 4 can be adjusted, while maintaining good development performance. Filming can be effectively prevented.

-Isocyanate compound-
In the present invention, the isocyanate compound used for prepolymerizing the silicone-modified polyol is not particularly limited as long as it has reactivity with the reactive group introduced into the silicone oil, but for example, , diisocyanates such as diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and modified products of these isocyanates, such as adduct type, bullet type, isocyanurate type, allophanate type, etc. Can be done. Among these isocyanate compounds, bifunctional isocyanate compounds, isocyanurate isocyanate compounds, and adduct isocyanate compounds are preferred, and these may be used alone or in combination. The longer the molecular chain of the isocyanate compound, the more flexible the polyurethane can be produced.

(B) Isocyanate compound As the isocyanate compound for curing the silicone-modified polyol, various isocyanate compounds commonly used in the preparation of polyurethane, such as aromatic isocyanate compounds, aliphatic isocyanate compounds, and alicyclic isocyanate compounds, can be used. Can be done.
Examples of aromatic isocyanate compounds include 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), and 4,4'-diphenylmethane diisocyanate (4,4-tolylene diisocyanate). '-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 1,4-phenylene diisocyanate, polymethylene polyphenylene polyisocyanate, toridine diisocyanate (TODI), 1,5-naphthalene diisocyanate (NDI), Examples include 3,3'-dimethylbiphenyl-4,4'-diisocyanate.
Examples of aliphatic isocyanate compounds include hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMHDI), lysine diisocyanate, methyl norbornene diisocyanate (NBDI), xylylene diisocyanate (XDI), and tetramethylxylylene diisocyanate. (TMXDI) and the like.
Furthermore, examples of alicyclic polyisocyanates include transcyclohexane-1,4-diisocyanate, isophorone diisocyanate (IPDI), H6XDI (hydrogenated XDI), H12MDI (hydrogenated MDI), and 4,4'-dicyclohexylmethane. Diisocyanates and the like can be mentioned.

In the present invention, the amount of the isocyanate compound used in the composition used to form the coating layer 4 is such that the reaction rate of the isocyanate compound is 80% or more and 126% or less, preferably 95% or more and 112% or less. It is preferable that

(C) Roughness agent The roughness agent used in the coating layer 4 is a particle having a siloxane bond or a urethane bond. Examples of such roughening agents include silicone rubber particles, polyurethane particles, and acrylic particles having urethane bonds. Heat-resistant and flexible silicone rubber particles, polyurethane particles, and acrylic particles having urethane bonds are preferred, and silicone rubber particles and acrylic particles having urethane bonds are more preferred.

The silicone rubber particles and urethane bond-containing acrylic particles used in the present invention preferably have heat resistance such that they do not deform or melt even at temperatures of 100°C or higher, and more preferably have heat resistance from 130°C to 180°C. . Thereby, even at the crosslinking temperature of the coating layer 4, these silicone rubber particles and acrylic particles having urethane bonds can be prevented from being deformed. To check the heat resistance of silicone rubber particles and acrylic particles with urethane bonds, use a melt flow indexer to confirm that the silicone rubber particles and acrylic particles with urethane bonds do not melt and flow out even when pressure and heat are applied. can be evaluated.

The hardness of the silicone rubber particles and the acrylic particles having urethane bonds is preferably 20 degrees or more and 80 degrees or less, and preferably 50 degrees or more and 75 degrees or less, as measured by durometer A (instantaneous) (JIS K 6253:1997). It is more preferable. Since the hardness of the silicone rubber particles and the acrylic particles having urethane bonds is within the above range, the friction coefficient of the coating layer 4 may increase due to destruction or deformation of the silicone rubber particles and the acrylic particles having urethane bonds. It is possible to effectively prevent the occurrence of adhesion, and it is also possible to prevent the occurrence of cracks and fractures in the coating layer 4 due to an excessive increase in the hardness of the coating layer 4, and it is also possible to prevent excessive stress from being applied to the toner.

The silicone rubber particles and acrylic particles may be present (buried) in the coating layer 4, or may be unevenly dispersed in the coating layer 4, or may be unevenly distributed on the surface side of the coating layer 4. Good too.

Among silicone rubber particles and acrylic particles having urethane bonds, silicone rubber particles preferably have a structure in which dimethylpolysiloxane, organopolysiloxane, or polyorganosilsesoxane is crosslinked; as acrylic particles having urethane bonds, Commercially available acrylic particles can be used.

For silicone rubber particles, organic groups include alkyl groups such as methyl, ethyl, propyl, and butyl groups; aryl groups such as phenyl and tolyl groups; alkenyl groups such as vinyl and allyl groups; β- Aralkyl groups such as phenylethyl group and β-phenylpropyl group; monovalent halogenated hydrocarbon groups such as chloromethyl group and 3,3,3-trifluoropropyl group; epoxy group, amino group, mercapto group, acryloxy group, Organopolysiloxane or organopolysilsesquioxane having one or more monovalent organic groups having 1 to 20 carbon atoms selected from reactive group-containing organic groups such as methacryloxy groups Particles prepared from these organopolysiloxanes or organopolysilsesquioxanes may be surface-treated with organoalkoxysilane. Examples of such silicone rubber particles include "KMP-597" manufactured by Shin-Etsu Chemical Co., Ltd., and "EP-5500", "EP-2600", and "EP-2601" manufactured by Dow Corning Toray Co., Ltd. , "E-2720", "DY 33-430M", "EP-2720", "EP-9215Cosmetic Powder", "9701Cosmetic Powder", etc. can be used.

The amount of silicone rubber particles and/or acrylic particles having urethane bonds used is preferably 15 parts by mass or more and 50 parts by mass or less, and 20 parts by mass or more and 45 parts by mass, based on 100 parts by mass of (A) silicone-modified polyol. It is more preferable that the amount is less than 1 part. By setting the amount of silicone rubber particles and/or acrylic particles having urethane bonds within the above-mentioned range, the surface roughness of the elastic roller 1 can be maintained appropriately, and developer transportability can be improved. At the same time, it is possible to maintain resolution at a high level and prevent deterioration of image quality.
The coating layer 4 may contain only one kind of roughness agent, or may contain two or more kinds of roughness agents.

The particle diameter of the silicone rubber particles and the acrylic particles having urethane bonds is preferably 0.2 μm or more and 10 μm or less, more preferably 0.8 μm or more and 5 μm or less. By setting the particle diameters of the silicone rubber particles and the acrylic particles having urethane bonds within the above range, the surface roughness of the elastic roller 1 can be maintained appropriately, and the developer transportability can be maintained well. , resolution can be maintained at a high level and deterioration of image quality can be prevented. The particle size of the silicone rubber particles and the acrylic particles having urethane bonds can be measured by cutting the elastic roller 1 and then observing the cross section with a microscope.

The thickness of the coating layer 4 is preferably 5 μm or more and 13 μm or less, more preferably 6 μm or more and 11 μm or less.

In the developing roller 1 of the present invention, the developing performance can be adjusted favorably by adjusting the electrical characteristics of the coating layer. Specifically, it is possible to adjust the resistance value and capacitance by combining the isocyanurate type and adduct type of the isocyanate compound.

(Adhesion of coating layer)
The coating layer 4 of the developing roller 1 of the present invention has an adhesion force of 4.0 μN or less, preferably 3.7 μN or less, determined by a nanoindentation method. When the adhesion force is 4.0 μN or less, the toner has good releasability and filming can be effectively prevented.

Here, the nanoindentation method is a method that uses a nanoindenter measurement device to push a diamond indenter into the sample surface to a certain load, and then measures the relationship between load and displacement until the indenter is removed. . Figure 3 shows a graph of typical loading and unloading curves measured by the nanoindenter. When the indenter is removed, a part of the unloading curve shows a negative load due to the adhesion force on the sample surface. The absolute value of the minimum negative load in the unloading curve is the adhesion force.
In the present invention, the adhesion force obtained by the nanoindentation method refers to a value measured under the conditions of the Examples described below.

(Resistance value of surface of coating layer)
The resistance value of the surface of the coating layer 4 of the developing roller 1 of the present invention is preferably 1×10 ⁷ Ω or more and 9×10 ⁹ Ω or less, and preferably 1×10 ⁷ Ω or more and 3×10 ⁹ Ω or less. is more preferable. When the resistance value is 9×10 ⁹ Ω or less, the image quality is good. The lower limit value of the resistance value is the limit resistance value that can be realized without a conductive agent.
The resistance value of the surface of the developing roller 1 can be adjusted by a combination of types of silicone-modified polyol and isocyanate compound of the coating layer 4. If necessary, the resistance value can be controlled by adding reactive ether-modified silicone oil.
The resistance value of the surface of the coating layer 4 is a value measured by the method described in Examples below.

(Capacitance of coating layer)
The capacitance of the coating layer of the developing roller is preferably 11 nF or less at 0.1 Hz, and from the viewpoint of maintaining good gradation of the resulting image density, the lower limit is preferably about 0.5 nF. . That is, the capacitance is more preferably 0.5 nF or more and 11 nF or less. When the capacitance is within the above range, the toner has good releasability and filming can be satisfactorily suppressed.
A conductivity imparting agent such as carbon or an ion conductive material is not used in the coating layer 4 because it causes an increase in capacitance, resulting in poor toner releasability.

(MD-1 hardness)
The MD-1 hardness of the coating layer is preferably 30° or more and 60° or less, more preferably 20° or more and 60° or less, and even more preferably 30° or more and 50° or less. By adjusting the MD-1 hardness of the coating layer within the above range, the amount of developer transported can be maintained while reducing the load on the developer.
To measure the MD-1 hardness, an MD-1 hardness meter ("Micro Rubber Hardness Meter MD-1" manufactured by Kobunshi Keiki Co., Ltd.) can be used. In the present invention, an MD-1 hardness meter is used on the roller surface. The MD-1 hardness is defined as the value read by pressing the indenter in peak hold mode with a hold time of 3 seconds.In principle, the MD-1 hardness meter is a type A durometer as described in JIS K6253. This is in accordance with.

(Hexadecane contact angle on the surface of the coating layer)
The hexadecane contact angle on the surface of the coating layer 4 of the developing roller 1 is preferably 30° or more, more preferably 43° or more, and even more preferably 50° or more. By setting the angle to 30° or more, it is possible to satisfactorily suppress the occurrence of filming. By suppressing filming, the life of the developing roller 1 is extended, leading to stabilization of image quality. It is also possible to suppress the occurrence of fogging due to filming.
The hexadecane contact angle can be measured using a portable contact angle meter PCA-1 (manufactured by Kyowa Interface Science).

(Other configurations)
The developing roller 1 of the present invention may include an adhesive layer between the shaft body 2 and the elastic layer 3 and between the elastic layer 3 and the covering layer 4. An adhesive layer may be provided between the elastic layer 3 and the coating layer 4 by irradiating the surface of the elastic layer 3 with UV light or the like and treating it with a primer, or surface modification and adhesion by plasma coating. The agent layer may be provided at the same time.

Hereinafter, the present invention will be described in detail by giving examples. Note that the present invention is not limited to the examples shown below.

[Example 1]
The developing roller of Example 1 was manufactured according to the following procedure.
(Formation of primer layer)
The shaft body (made by SUM23, diameter 7.5 mm, length 274.1 mm) that has been subjected to electroless nickel plating treatment is cleaned with ethanol, and its surface is coated with a silicone primer (product name "Primer No. 16", Shin-Etsu Chemical). (manufactured by Kogyo Co., Ltd.) was applied. The primer-treated shaft was baked at a temperature of 150° C. for 10 minutes using a gear oven, and then cooled at room temperature for 30 minutes or more to form a primer layer on the outer peripheral surface of the shaft.

(Formation of elastic layer)
An elastic body made of a rubber material was molded on the outer peripheral surface of the shaft by extrusion molding using a millable silicone rubber composition. In the extrusion molding, the silicone rubber composition was heated at 270° C. for 5 minutes using an external heating furnace (IR furnace), and then heated at 200° C. for 4 hours using a gear oven to cure it. As a result, an elastic layer made of a cured rubber composition was formed on the outer circumferential surface of the primer-treated shaft. The elastic layer was a solid layer, and the thickness of the elastic layer was 4.25 mm.

(Formation of coating layer)
First, three types of silicone-modified polyols A, B, and C were synthesized by holding the compounds shown below in the mass parts shown in Table 1 at 100°C to 120°C for 4 to 6 hours.
a1 Dimethyl silicone oil modified with hydroxyl groups at both ends a2 Silicone oil modified with diol at one end a3 Isocyanate compound Isocyanurate type a4 Isocyanate compound Adduct type a5 Isocyanate compound Bifunctional type

A coating layer composition was prepared using the following materials and having the formulation shown in Table 2. The base resin was a silicone-modified urethane resin formed from the following silicone-modified polyol and isocyanate.
・The above silicone-modified polyols A, B, and C
・Isocyanate “TPA-100” (product name, manufactured by Asahi Kasei Corporation)
"E402-80B" (product name, manufactured by Asahi Kasei Corporation)
・Roughness agent (product name "EP-2601", manufactured by Dow Corning Toray Co., Ltd.)
A catalyst and a thinner are appropriately added to the composition for the upper coating layer.

Next, the outer peripheral surface of the elastic layer was subjected to UV treatment. Thereafter, a coating layer composition was applied onto the UV-treated elastic layer by a spray method. The applied composition was heated at 150°C to 160°C for 30 minutes to obtain a developing roller.
The thickness of the coating layer after drying was 9 μm.

[Examples 2, 3, 4 and Comparative Example 1]
A developing roller was produced in the same manner as in Example 1 except that a coating layer was formed using the formulation shown in Table 2.

[evaluation]
The following evaluations were performed for the above Examples and Comparative Examples. The evaluation results are shown in Table 2.

(Measurement of adhesion force)
The adhesion of the coating layer was measured as follows.
Using the nanoindentation method, the absolute value of the minimum negative load in the unloading curve was determined under the following conditions using a nanoindenter measurement device (product name: Hysitron TI Premier, manufactured by Bruker), and this was It was taken as the adhesion force of the coating layer.
Measurement indenter: Conical indenter, nominal radius 4 to 6 μm, cone angle 60°, Young's modulus 1140 GPa, Poisson's ratio 0.07
Measurement environment: temperature 23℃, relative humidity 50%RH
Load application acceleration: 50 μN/10 seconds Maximum load holding time: 10 seconds Unloading speed: -50 μN/10 seconds

(capacitance)
The capacitance of the coating layer was measured as follows.
Using an LCR meter (manufactured by NF Circuit Design Block Co., Ltd.), an electrode was made with conductive paste on the surface of the developing roller on which the coating layer was formed, and the conductive paste and core were The capacitance between them was measured using an LCR meter.

(MD-1 hardness)
Using an MD-1 hardness meter (manufactured by Kobunshi Keiki Co., Ltd., "Micro Rubber Hardness Meter MD-1"), press the indenter of the MD-1 hardness meter against the surface of the developing roller, set the peak hold mode, and set the hold time to 3. MD-1 hardness was measured.

(Hexadecane contact angle)
Hexadecane was set in the device, droplets of hexadecane were dropped onto the developing roller, and the contact angle of hexadecane was measured using a portable contact angle meter PCA-1 (manufactured by Kyowa Kaimen Kagaku).

(Resistance value)
The surface resistance values of the coating layers of the above Examples and Comparative Examples were measured. FIG. 2 shows a schematic front view of the measuring device.
As shown in FIG. 2, the developing roller 1 is placed on a gold-plated plate 51, and weights 52 weighing 500 g are hung on both ends. / Measured using a microcurrent meter "5450" (manufactured by ADC Co., Ltd.) 54.

(Filming evaluation)
The filming status after printing 4000 sheets using a monochrome image forming apparatus (trade name "HL-L2360DN", manufactured by Brother Industries, Ltd.) was evaluated.
Filming was evaluated based on the amount of developer attached. Specifically, after 4000 sheets were printed, the developer adhering to the surface of the developing roller was sucked, and then the mass transferred to a filming weight measuring jig was measured. Regarding the filming evaluation, the mass of the transferred developer was evaluated using the following evaluation criteria. If the filming evaluation is A, it is passed.
A: 0.00mg/ ^cm2 or more and 0.03mg/ ^cm2 or less B: More than 0.03mg/ ^cm2 and 0.06mg/ ^cm2 or less C: More than 0.06mg/ ^cm2

(Toner releasability evaluation)
The developing rollers of the above Examples and Comparative Examples were attached to the cartridge of a monochrome image forming apparatus (product name "HL-L2360DN", manufactured by Brother Industries, Ltd.), and the cartridge electrodes were installed in a low temperature, low humidity environment (10° C., 20% RH). It was connected to an external power source and the print density was measured while varying the voltage. Print density was measured for the solid printed area using an X-Rite 504 spectrodensitometer manufactured by X-Rite.
Print density was evaluated using the following evaluation criteria. It was determined that the higher the density, the better the toner releasability even at low voltage. In the present invention, a case where the external voltage was 210V and the evaluation was A was considered to be a pass.
A: 1.4 or more B: 1.35 or more C: less than 1.35

As shown in Table 2, the developing roller of the present invention has an adhesion force of 4.0 μN or less determined by the nanoindentation method of the coating layer, so that the toner releasability at an external voltage of 210 V is rated A. Therefore, filming can be effectively suppressed. Therefore, the developing roller of the present invention can contribute to providing high-quality images over a long period of time.

1 Developing roller 2 Shaft body 3 Elastic layer 4 Covering layer 51 Gold plated plate 52 Weight 53 Shaft 54 Ultra high resistance/micro ammeter

Claims (5)

A developing roller comprising a shaft, an elastic layer provided on an outer surface of the shaft, and a coating layer provided outside the elastic layer,
The developing roller has an adhesion force of the coating layer determined by a nanoindentation method of 4.0 μN or less, and a print density of 1.4 or more at an external voltage of 210 V, as measured by the following measuring method.
<Measurement method>
In a monochrome image forming apparatus (product name "HL-L2360DN", manufactured by Brother Industries, Ltd.), a developing roller is attached to the cartridge, and the cartridge electrode is connected to an external power source in a low temperature, low humidity environment (10° C., 20% RH). The print density of the solid print area when changing the voltage is measured using an X-Rite 504 spectrodensitometer manufactured by X-Rite. The developing roller according to claim 1, wherein the capacitance of the coating layer is 11 nF or less at 0.1 Hz. The developing roller according to claim 1 or 2, wherein the MD-1 hardness of the coating layer is 30° or more and 60° or less. 4. The developing roller according to claim 1, wherein a contact angle of hexadecane on the surface of the developing roller is 30 degrees or more. The coating layer includes a silicone-modified urethane resin,
5. The developing roller according to claim 1, wherein the surface resistance value of the developing roller is 1×10 ⁷ Ω or more and 9×10 ⁹ Ω or less.

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