CN112782950A

CN112782950A - Developing roller

Info

Publication number: CN112782950A
Application number: CN202011233074.1A
Authority: CN
Inventors: 山下聪太郎; 藤泽祐辅
Original assignee: Bridgestone Corp
Current assignee: Arkema Co ltd
Priority date: 2019-11-06
Filing date: 2020-11-06
Publication date: 2021-05-11
Also published as: JP2021076654A

Abstract

The invention provides a developing roller capable of inhibiting fog and toner contamination while maintaining good initial image density, the developing roller (1) is characterized by comprising a mandrel member (2), an elastic layer (3) arranged on the outer side of the mandrel member (2) in the radial direction, and a surface layer (4) arranged on the outer side of the elastic layer (3) in the radial direction, wherein the surface layer (4) comprises a thermosetting urethane resin, carbon black and a metal-containing urethane reaction catalyst, the thermosetting urethane resin is formed by reacting a polyol component and a polyisocyanate component, the carbon black has an average particle diameter of 120-160 nm and a DBP oil absorption of 900mL/100g or more, and the carbon black content is 3-5 parts by mass relative to 100 parts by mass of the polyol component of the thermosetting urethane resin.

Description

Developing roller

Technical Field

The present invention relates to a developing roller.

Background

In an electrophotographic image forming apparatus such as a copying machine and a printer, a pressure development method is known as a developing method for supplying toner to a photosensitive drum holding a latent image and visualizing the latent image by adhering the toner to the latent image on the photosensitive drum. In this pressure development method, for example, a photosensitive drum is charged at a constant potential, an electrostatic latent image is formed on the photosensitive drum by an exposure device, a developing roller carrying toner is brought into contact with the photosensitive drum holding the electrostatic latent image, and toner is attached to the latent image on the photosensitive drum to develop the latent image.

In the above-described pressure development method, since the developing roller must be rotated while being kept in a state of being in close contact with the photosensitive drum, a semiconductive elastomer in which a conductive agent is dispersed in an elastomer such as urethane or an elastic layer formed of a foam obtained by foaming the elastomer is formed on the outer periphery of a mandrel member formed of a good conductive material such as metal. Further, for the purpose of controlling the chargeability and adhesion to the toner, preventing contamination of the photosensitive drum by the elastic layer, and the like, a surface layer made of a resin or the like may be further formed on the surface of the elastic layer (see patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication (JP 2015-232723)

Disclosure of Invention

Problems to be solved by the invention

Recently, images with higher speed (high speed printing), longer durability (high durability), and higher image quality have been demanded. In order to meet this demand, when printing is performed in a severe environment, there is a problem in that toner easily leaks from an end sealing member of a developing device incorporated into a developing roller.

As a result of intensive studies, the present inventors have found that toner leakage can be improved by applying fine particles having a glass transition temperature, an average particle diameter, and universal hardness (universal hardness) in a specific range to the surface layer. However, it was found that if this method is employed, the image generates fog in a low-temperature and low-humidity environment (LL environment).

In contrast, the present inventors have further studied to suppress fog, but even if fog is successfully suppressed, the initial image density deteriorates, or toner contamination further occurs, and it is difficult to suppress fog based on suppression of toner contamination while maintaining a good initial image density.

Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a developing roller which can suppress fog and toner contamination while maintaining a good initial image density.

Means for solving the problems

The main aspects of the present invention to solve the above problems are as follows.

The developing roller of the present invention is characterized by comprising a mandrel member, an elastic layer arranged on the outer side of the mandrel member in the radial direction, and a surface layer arranged on the outer side of the elastic layer in the radial direction,

the surface layer contains a Thermosetting urethane resin (Thermosetting urethane resin), carbon black, and a metal-containing urethane reaction catalyst,

the thermosetting urethane resin is obtained by reacting a polyol component with a polyisocyanate component,

the carbon black has an average particle diameter of 120 to 160nm and a DBP oil absorption of 900mL/100g or more,

the content of the carbon black is 3 to 5 parts by mass per 100 parts by mass of the polyol component of the thermosetting urethane resin.

The developing roller of the present invention can suppress fog and toner contamination while maintaining a good initial image density.

In a preferred example of the developing roller of the present invention, the metal-containing urethane-forming reaction catalyst is a tin compound. In this case, toner contamination can be further suppressed.

In the developing roller of the present invention, it is preferable that the surface layer has a universal hardness of 0.4N/mm at a penetration depth of 10 μm²The following. In this case, fogging can be further suppressed.

In the developing roller of the present invention, it is preferable that the thermosetting urethane resin is obtained by further reacting a urethane prepolymer synthesized from a mixture of a polyol component and a polyisocyanate component with a polyol component and/or a polyisocyanate component, and an isocyanate index (NCO/OH) of the mixture of the polyol component and the polyisocyanate component used in the synthesis of the urethane prepolymer is 0.1 to 0.2. In this case, fog can be further suppressed.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a developing roller that can suppress fog and toner contamination while maintaining a good initial image density can be provided.

Drawings

Fig. 1 is a sectional view of an example of a developing roller of the present invention.

Description of the reference numerals

1: developing roller, 2: spindle member, 3: elastic layer, 4: surface layer

Detailed Description

< developing roller >

Hereinafter, the developing roller of the present invention will be described in detail by way of example based on embodiments thereof.

Fig. 1 is a sectional view of an example of a developing roller of the present invention. The developing roller 1 illustrated in the figure includes a mandrel member 2, an elastic layer 3 disposed on the outer side of the mandrel member 2 in the radial direction, and a surface layer 4 disposed on the outer side of the elastic layer 3 in the radial direction. Note that the developing roller 1 shown in fig. 1 has only one elastic layer 3, but the developing roller of the present invention may have two or more elastic layers. Further, the developing roller 1 shown in fig. 1 is provided with the surface layer 4 on the outer peripheral surface of the elastic layer 3, but the developing roller of the present invention may have another layer between the elastic layer 3 and the surface layer 4.

The surface layer 4 of the developing roller 1 of the present invention is characterized in that it comprises a thermosetting urethane resin obtained by reacting a polyol component with a polyisocyanate component, carbon black having an average particle diameter of 120 to 160nm and a DBP oil absorption of 900mL/100g or more, and a metal-containing urethane reaction catalyst, and the content of the carbon black is 3 to 5 parts by mass per 100 parts by mass of the polyol component of the thermosetting urethane resin.

The surface layer 4 of the developing roller 1 of the present invention contains a thermosetting urethane resin and carbon black, and the content of the carbon black is 5 parts by mass or less with respect to 100 parts by mass of the polyol component constituting the thermosetting urethane resin, so that the hardness is low and the toner layer formed of the toner can be further controlled. Further, by further controlling the toner layer, the toner conveying amount can be reduced, and fogging of the image can be suppressed.

When the content of carbon black is merely reduced, the resistance value of the surface layer 4 increases, the initial image density deteriorates, and toner contamination deteriorates. On the other hand, in the surface layer 4 of the developing roller 1 of the present invention, the conductivity of the surface layer 4 is improved and a good initial image density is maintained by containing carbon black having an average particle diameter of 120 to 160nm and a DBP oil absorption of 900mL/100g or more in an amount of 3 parts by mass or more with respect to 100 parts by mass of the polyol component constituting the thermosetting urethane resin. Here, the carbon black having an average particle diameter of 120 to 160nm and a DBP oil absorption of 900mL/100g or more is excellent in conductivity, and therefore, the conductivity of the surface layer 4 can be improved. In addition, in the surface layer 4 of the developing roller 1 of the present invention, the urethane reaction of the polyol component and the polyisocyanate component is promoted by containing the metal-containing urethane reaction catalyst, thereby suppressing the loss of the toner on the surface layer 4 and suppressing the toner contamination.

Therefore, the developing roller 1 of the present invention can suppress fog and toner contamination while maintaining a good initial image density.

< mandrel Member >

The mandrel member 2 is preferably a member having good electrical conductivity. As the mandrel member 2, for example, a mandrel made of a solid body made of metal such as iron, stainless steel, or aluminum, a metal mandrel made of metal such as a cylindrical body made of metal with a hollow portion formed therein, a mandrel made of plastic having good conductivity, or the like can be used.

< elastic layer >

The elastic layer 3 is preferably formed of an elastomer, and more preferably formed of a foam of an elastomer. For example, the elastic layer 3 may be formed of an elastomer such as polyurethane, silicone rubber, ethylene-propylene-diene rubber (EPDM), nitrile rubber (NBR), Natural Rubber (NR), styrene-butadiene rubber (SBR), Butadiene Rubber (BR), Isoprene Rubber (IR), polynorbornene rubber, butyl rubber (IIR), Chloroprene Rubber (CR), acrylic rubber, epichlorohydrin rubber (ECO), ethylene-vinyl acetate copolymer (EVA), and a mixture thereof. Among these elastomers, polyurethane is preferably used for the elastic layer 3. Since the surface layer 4 contains a thermosetting urethane resin, if polyurethane is used for the elastic layer 3, the adhesion between the elastic layer 3 and the surface layer 4 is good.

The foam constituting the elastic layer 3 may be formed by chemically foaming the elastomer using a foaming agent, mechanically enclosing air and foaming the elastomer like a urethane foam, or the like. The foaming ratio of the foam constituting the elastic layer 3 is preferably in the range of 1.5 to 50 times, and the density is preferably 0.05 to 0.9g/cm³The range of (1).

Further, since the compression set performance is improved by making the cells of the foam constituting the elastic layer 3 closed cells, the cells in the foam are preferably closed cells. Here, in order to make the foam cells as closed cells, a method of foaming the raw material of the elastomer by mechanical agitation to produce a foam can be suitably employed.

The elastic layer 3 is preferably blended with a conductive agent to adjust conductivity. Examples of the conductive agent used for the elastic layer 3 include an electron conductive agent and an ion conductive agent. The conductive agent can be used alone in 1 kind, can also be used in 2 or more kinds in combination, can also be used in combination with electron conductive agent and ion conductive agent.

Examples of the electron conductive agent include: conductive carbon such as ketjen black and acetylene black, carbon black for rubber such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, MT, color carbon black subjected to oxidation treatment or the like, pyrolytic carbon black, natural graphite, artificial graphite, metal oxides such as antimony-doped tin oxide, ITO, tin oxide, titanium oxide, zinc oxide, metals such as nickel, copper, silver, germanium, conductive polymers such as polyaniline, polypyrrole, polyacetylene, conductive whiskers such as carbon whiskers, graphite whiskers, titanium carbide whiskers, conductive potassium titanate whiskers, conductive barium titanate whiskers, conductive titanium oxide whiskers, conductive zinc oxide whiskers, and the like.

Examples of the ion conductive agent include: ammonium salts such as perchlorates, chlorates, hydrochlorides, bromates, iodates, fluoroborates, sulfates, ethylsulfates, carboxylates, and sulfonates of tetraethylammonium, tetrabutylammonium, dodecyltrimethylammonium, hexadecyltrimethylammonium, benzyltrimethylammonium, and modified fatty acid dimethylethylammonium; alkali metal and alkaline earth metal perchlorates such as lithium, sodium, potassium, calcium and magnesium, chlorates, hydrochlorides, bromates, iodates, fluoroborates, sulfates, trifluoromethylsulfates and sulfonates.

The amount of the electron conductive agent is preferably 1 to 50 parts by mass, and more preferably 5 to 40 parts by mass, based on 100 parts by mass of the resin component constituting the elastic layer 3. The amount of the ionic conductive agent is preferably 0.01 to 10 parts by mass, and more preferably 0.05 to 5 parts by mass, based on 100 parts by mass of the resin component constituting the elastic layer 3.

The elastic layer 3 is preferably made to have a resistance value of 10 by blending a conductive agent³～10¹⁰Omega cm, more preferably to 10⁴～10⁸Omega cm. The resistance value of the elastic layer 3 is 10³In the case of Ω cm or more, leakage of electric charge to the photosensitive drum or the like can be suppressed, and also, the developing roller itself can be prevented from being broken by voltage, and in addition, 10 is used¹⁰When Ω cm or less, the generation of fog can be further suppressed.

In order to make the elastomer a rubber-like material, the elastic layer 3 may contain a crosslinking agent such as an organic peroxide, a vulcanizing agent such as sulfur, a vulcanization aid, a vulcanization accelerator, a vulcanization acceleration aid, a vulcanization retarder, and the like, as necessary. The elastic layer 3 may further contain various rubber compounding agents such as fillers, peptizers, foaming agents, plasticizers, softeners, adhesion-imparting agents, releasing agents, release agents, extenders, and colorants.

< surface layer >

The surface layer 4 contains a thermosetting urethane resin, a metal-containing urethane reaction catalyst, and carbon black. Here, the thermosetting urethane resin is obtained by reacting a polyol component with a polyisocyanate component, and has a property of being cured by heat.

The thermosetting urethane resin used in the surface layer 4 is preferably obtained by further reacting a urethane prepolymer synthesized from a mixture of a polyol component and a polyisocyanate component with a polyol component and/or a polyisocyanate component. In the synthesis of the urethane prepolymer, a part of the polyol component and/or the polyisocyanate component may be unreacted. When the urethane prepolymer is further reacted with the polyol component and/or the polyisocyanate component, the polyol component and/or the polyisocyanate component may be further added to the unreacted polyol component and/or polyisocyanate component to carry out the reaction.

The isocyanate index (NCO/OH) of the mixture of the polyol component and the polyisocyanate component used for the synthesis of the urethane prepolymer is preferably 0.1 to 0.2. Here, the isocyanate index (NCO/OH) is the ratio of the isocyanate groups (NCO) of the polyisocyanate component to the hydroxyl groups (OH) of the polyol component in the mixture. When the isocyanate index (NCO/OH) is 0.1 or more, the reaction of the polyol component and the polyisocyanate component can be sufficiently ensured, and when the isocyanate index (NCO/OH) is 0.2 or less, the hardness of the surface layer 4 can be made lower, the toner conveying amount can be reduced, and the fogging can be further suppressed.

Examples of the polyol component include: polyether polyols obtained by addition polymerization of alkylene oxides such as ethylene oxide and propylene oxide to glycerin, polytetramethylene glycol, glycerin, ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, octylene glycol, polybutadiene polyol, polyisoprene polyol, polyester polyol, and the like.

The polyol component is preferably a lactone-modified polyol. The lactone-modified polyol can be produced by modifying the terminal of a polyol with a lactone such as epsilon-caprolactone, or can be a commercially available product. The lactone-modified polyol preferably has a number average molecular weight (Mn) in terms of polystyrene as measured by gel permeation chromatography of 1000 to 5000, more preferably 1000 to 3000, and a molecular weight distribution (Mw/Mn) represented by the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in terms of polystyrene as measured by gel permeation chromatography of preferably 2.5 or less, more preferably 2.0 or less.

Examples of the polyisocyanate component include: isophorone diisocyanate (IPDI), Toluene Diisocyanate (TDI), diphenylmethane diisocyanate (MDI), crude diphenylmethane diisocyanate (crude MDI), hydrogenated diphenylmethane diisocyanate, hydrogenated toluene diisocyanate, Hexamethylene Diisocyanate (HDI), urethane-modified hexamethylene diisocyanate, and the like. As the polyisocyanate component, isophorone diisocyanate (IPDI) is preferably used in combination with other polyisocyanates, isophorone diisocyanate is more preferably used in combination with hexamethylene diisocyanate, and isophorone diisocyanate and hexamethylene diisocyanate are particularly preferably used in a ratio of 3: 1-1: 3 in a molar ratio.

The carbon black used in the surface layer 4 has an average particle diameter of 120 to 160nm and a DBP oil absorption of 900mL/100g or more, and functions as a conductive agent. The carbon black has a larger average particle diameter, a larger DBP oil absorption, and higher conductivity than conventional carbon black.

In the present invention, the average particle diameter of carbon black is determined by observing the carbon black with a transmission electron microscope at a magnification of 100 ten thousand times and calculating the number average of the area equivalent diameter of primary particles of 100 carbon blacks.

In the present invention, the DBP oil absorption of carbon black is measured according to method A of JIS K6221(1982) 6.1.2.

The content of the carbon black is 3 to 5 parts by mass per 100 parts by mass of the polyol component of the thermosetting urethane resin. By setting the carbon black content to 3 parts by mass or more, the conductivity of the surface layer 4 can be improved, and a good initial image density can be maintained. Further, by setting the content of carbon black to 5 parts by mass or less, the surface layer 4 can be made low in hardness, the toner conveyance amount can be reduced, and fogging can be suppressed.

Here, the content of carbon black is preferably 3.5 parts by mass or more from the viewpoint of the initial image density and toner contamination. The content of carbon black is preferably 4.5 parts by mass or less from the viewpoint of suppression of fogging.

The metal-containing urethane reaction catalyst used in the surface layer 4 contains a metal and has a catalytic action of promoting the urethane reaction between the polyol component and the polyisocyanate component. Examples of the metal-containing urethane reaction catalyst include: tin compounds, titanium compounds, bismuth compounds, lead compounds, zirconium compounds, and the like. More specifically, there may be mentioned: tin compounds such as dibutyltin dilaurate, dibutyltin diacetate, dibutyltin thiocarboxylate, dibutyltin dimaleate, dioctyltin thiocarboxylate, tin octenoate, dibutyltin, monobutyltin oxide, and stannous chloride; titanium compounds such as tetrabutyl titanate, tetraethyl titanate, and tetraisopropyl titanate; bismuth compounds such as bismuth octylate and inorganic bismuth; lead compounds such as lead octenoate; zirconium compounds such as zirconium tetraacetylacetonate; and so on. These metal-containing urethane reaction catalysts may be used alone in 1 kind, or 2 or more kinds may be used in combination. Among these, tin compounds are preferable from the viewpoint of excellent catalytic action in the urethanization reaction and prevention of toner contamination.

The content of the metal-containing urethane reaction catalyst is preferably 0.0001 parts by mass or more and preferably 1 part by mass or less with respect to 100 parts by mass of the polyol component of the thermosetting urethane resin. If the content of the metal-containing urethanization reaction catalyst is 0.0001 parts by mass or more, the effect of suppressing toner contamination increases. Further, if the content of the metal-containing urethane reaction catalyst is too large, the effect is saturated, and therefore, from the viewpoint of cost, it is preferably 1 part by mass or less.

The surface layer 4 preferably contains microparticles. By including the fine particles in the surface layer 4, friction with other members such as a developing blade and damage to toner can be reduced.

The glass transition temperature (Tg) of the fine particles is preferably-10 ℃ or lower, more preferably-30 ℃ or lower, and still more preferably-50 ℃ or lower. In the case where the surface layer 4 contains fine particles having a low Tg, friction with the developing roller and other members, such as the developing blade, can be further reduced. Further, by reducing the friction, damage to the toner can be further reduced, and the occurrence of development streaks and films on the developing roller can be suppressed by suppressing the fusion of the toner to the developing roller or the developing blade. The material of the fine particles is preferably a polyurethane resin.

The average particle diameter of the fine particles is preferably 20 μm or more, more preferably 20 to 25 μm. In general, in the end sealing member of the developing device, a surface that is rubbed against the surface of the axial (longitudinal) end of the developing roller is formed of a flexible member such as a pile or electrostatic flocking formed by weaving felt or fibers, and the flexible member is brought into pressure contact with the surface layer 4 of the developing roller to exhibit sealing properties. By using fine particles having an average particle diameter of 20 μm or more, the surface layer 4 of the developing roller is roughened, the end sealing member easily scrapes off the toner, and leakage of the toner from the end sealing member can be suppressed. The average particle size of the fine particles can be determined by a dynamic light scattering method.

The content of the fine particles is preferably 5.0 to 15.0 parts by mass, more preferably 7.0 to 10.0 parts by mass, per 100 parts by mass of the polyol component of the thermosetting urethane resin. When the content of the fine particles is 5.0 parts by mass or more, the scraping effect of the toner can be sufficiently obtained, and when the content of the fine particles is 15.0 parts by mass or less, the friction between the fine particles and the toner can be reduced.

The particles are preferably pressed into a depth of 20 μm and have a universal hardness of 0.8N/mm²The content is more preferably 0.2 to 0.8N/mm²More preferably 0.4 to 0.6N/mm². Universal hardness of the particles is 0.8N/mm²In the following case, the load on the toner is small, and damage to the toner can be reduced. The universal hardness of the fine particles can be obtained by measuring the fine particle portion in the surface layer 4 using a FISHER hardness tester.

The surface layer 4 may further contain a resin other than the thermosetting urethane resin, a conductive agent other than the carbon black, and the like in addition to the above components.

The surface layer 4 preferably has a universal hardness of 0.4N/mm at an indentation depth of 10 μm²Hereinafter, more preferably 0.35N/mm²The following. Universal hardness at 10 μm penetration depth of 0.4N/mm²In the following case, the hardness of the surface layer 4 is sufficiently low to further suppress fogging. In the present invention, the universal hardness of the surface layer 4 is calculated from the load applied by the indenter when the indenter is pressed into the surface layer 4 by using a FISHER hardness tester and the contact area between the indenter and the surface layer 4 when the pressing depth reaches 10 μm.

The surface layer 4 preferably has a thickness of 30 μm or less, more preferably 1 to 15 μm. When the thickness of the surface layer 4 is 30 μm or less, the surface layer 4 has high flexibility, and damage to the toner is suppressed, so that the toner is prevented from being fixed to the photosensitive drum or the developing blade, and a good image is formed.

The method for forming the surface layer 4 is not particularly limited, and the following method is preferably used: a coating composition containing each component constituting the surface layer 4 is prepared, and the coating composition is applied by a known coating method such as a dipping method, a spraying method, a roll coating method, and the like, and then cured by heating at 100 to 120 ℃ for 20 to 40 minutes.

< other layer >

An intermediate layer (not shown) may be formed as another layer provided between the elastic layer 3 and the top sheet 4. For example, by providing an intermediate layer formed softer than the surface layer 4, damage to the toner can be further suppressed. The intermediate layer can be formed using any 1 or 2 or more kinds of aqueous resins selected from rubbers, urethanes, and acrylics. As the rubber, latex such as Natural Rubber (NR), Chloroprene Rubber (CR), nitrile rubber (NBR), styrene-butadiene rubber (SBR) and the like can be suitably used, as the urethane, emulsion or dispersion such as ether urethane, ester urethane and the like can be suitably used, and as the Acrylic, emulsion such as Acrylic (Acrylic) or Acrylic styrene (Acrylic styrene) can be suitably used.

< Properties of developing roller >

The surface roughness of the developing roller of the present invention is preferably such that JIS arithmetic mean roughness (Ra) is 0.7 to 2.0. mu.m. When the arithmetic mean roughness (Ra) of the developing roller is 2.0 μm or less, the charge amount of the toner is sufficient, and the occurrence of fog and gradation failure in an image can be suppressed. Further, in the case where the arithmetic average roughness (Ra) is 0.7 μm or more, the toner can be sufficiently prevented from leaking from the end sealing member of the developing device.

The resistance value of the developing roller of the present invention is preferably 10 from the viewpoint of obtaining a good image³～10¹⁰Omega, more preferably 10⁴～10⁸Omega. Resistance value at the developing roller was 10³When Ω or more, the gradation is easily controlled, and even when the photosensitive drum has a defect, the bias leakage is less likely to occur. Further, the resistance value was 10¹⁰When Ω or less, for example, when toner is developed on the photosensitive drum, a developing bias sufficient for development can be secured, and a sufficient image density can be obtained.

The measurement of the resistance value may be obtained, for example, by pressing the outer peripheral surface of the developing roller against a flat plate or cylindrical counter electrode with a predetermined pressure, applying a voltage of 100V or 50V between the mandrel and the counter electrode, and then measuring the current value.

Further, the developing roller of the present invention is preferably 60 ° or less in Asker C hardness. By making the developing roller low in hardness of Asker C hardness of 60 ° or less, it is possible to prevent toner from being damaged between the developing roller and the photosensitive drum, the developing blade, the toner supply roller, and the like when assembled into the image forming apparatus, and to form a sufficiently good image.

< uses of developing roller >

The developing roller of the present invention can be used in various image forming apparatuses of electrophotographic system such as copying machines, facsimile machines, and Laser Beam Printers (LBP). The image forming apparatus generally includes a photosensitive drum for holding an electrostatic latent image, a charging member located in the vicinity of the photosensitive drum for charging the photosensitive drum, a toner supply roller for supplying toner, a transfer member located in the vicinity of the photosensitive drum, and a cleaning member disposed adjacent to the photosensitive drum, and further includes a developing roller between the toner supply roller and the photosensitive drum. Further, a developing blade (also referred to as a "layer-forming blade") is generally provided in the vicinity of the developing roller.

In an image forming apparatus, after a voltage is applied between a photosensitive drum and a charging member to charge the photosensitive drum to a certain potential, an electrostatic latent image is formed on the photosensitive drum by an exposure machine. Then, the toner is sent from the toner supply roller to the photosensitive drum through the developing roller. At this time, the toner on the developing roller is adjusted to a uniform thin layer by the developing blade, and the developing roller rotates while contacting the photosensitive drum, so that the toner adheres to the electrostatic latent image on the photosensitive drum from the developing roller, and the latent image is visualized. The toner adhering to the latent image is transferred to a recording medium such as paper by a transfer member, and the toner remaining on the photosensitive drum after the transfer is removed by a cleaning member.

Here, by using the developing roller of the present invention described above in an image forming apparatus, the toner conveyance amount from the developing roller to the photosensitive drum can be reduced, and fog can be suppressed. Further, since the developing roller has sufficient conductivity, a good initial image density can be maintained, and further, since the urethane-forming reaction in the surface layer 4 is promoted, damage to the toner can be suppressed, and contamination of the toner can be prevented.

Examples

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

< production of roll body >

Toluene Diisocyanate (TDI) was mixed with 100 parts by mass of acetylene BLACK (product name "DENKA BLACK" manufactured by electrochemical Co., Ltd.) in an amount of 2 parts by mass to prepare toluene diisocyanate in which acetylene BLACK was dispersed, and this toluene diisocyanate was referred to as component A.

On the other hand, 15 parts by mass of polyether polyol (trade name "excenol 420", manufactured by Asahi-Olin Ltd.), 10 parts by mass of polyether polyol (trade name "excenol 430", manufactured by Asahi glass Co., Ltd.), and sodium perchlorate (NaClO)₄)0.1 part by mass of polyether is further modified by mixing while heating to 70 DEG C4.5 parts by mass of a silicone oil (foam stabilizer, trade name "SF 2937F" available from Toray corporation) and 0.2 part by mass of dibutyltin dilaurate (catalyst) were mixed to prepare a mixture, which was referred to as component B.

Next, the above-mentioned a component and B component were foamed by a mechanical foaming method, and further injected into a cylindrical mold with a mandrel attached thereto, and a roller body having an elastic layer made of foamed polyurethane was produced by RIM molding.

< formation of surface layer >

A polyisocyanate (trade name "paccel 220 AL", manufactured by seikagaku corporation) was blended with 100 parts by mass of a polyol (Daicel Chemical Industries, ltd.) so as to have an isocyanate index shown in table 1, and the mixture was heated to synthesize a urethane prepolymer.

To the obtained urethane prepolymer, polyisocyanate (trade name "excelhardenerer HX", manufactured by seikagaku corporation) was further added so that the total amount of polyisocyanate used was 50 parts by mass, and carbon black, a catalyst and fine particles were further added in the amounts shown in table 1 to prepare a coating composition for a surface layer.

The resulting coating composition was applied to the elastic layer, and cured by heating at 115 ℃ for 30 minutes to form a surface layer, thereby obtaining the developing rollers of examples and comparative examples.

< measurement and evaluation of resistance value, Universal hardness, initial image Density, fog, toner contamination >

The resistance value and universal hardness of the obtained developing roller were measured by the following methods, and the initial image density, fog, and toner contamination were evaluated. The results are shown in Table 1.

(1) Resistance value

The outer peripheral surface of the developing roller was pressed against a cylindrical counter electrode with a predetermined pressure, a voltage of 50V was applied between the spindle member and the counter electrode, and the resistance value was measured from the current value at that time.

(2) Universal hardness

The universal hardness of the surface layer was measured by pressing a vickers indenter into the surface layer using a FISHER hardness tester H100C, and using the load applied by the indenter when the pressing depth reached 10 μm and the area of contact between the indenter and the surface layer.

(3) Initial image density

Each of the obtained rollers was assembled into a printer "LBP 651C" manufactured by canon corporation, and a full black image was printed. The obtained image was measured by an X-Rite inc.

If the numerical value is in the range of 1.2 to 1.5, it means that the initial image density is good.

(4) Fog mist

Each of the obtained rolls was assembled in a printer "LBP 651C" manufactured by canon corporation under LL atmosphere (15 ℃, 10% RH), and subjected to durable printing of 1 ten thousand 2000 sheets, to output a full white image. The obtained images were evaluated according to the following criteria.

Good: it was not confirmed that toner was fixed on the image

X: it can be confirmed that toner is fixed on the image

(5) Contamination of toner

After the developing roller was left to stand in an environment of 45 ℃ and 72% RH for 1 week in a state where the surface of the developing roller was fully coated with the toner, the toner was blown off by blowing air, and the toner contamination was evaluated according to the following criteria.

Good: in the case where no toner was observed on the surface of the developing roller

And (delta): in the case where toner slightly remains on the surface of the developing roller

X: in the case where toner is fixed to the surface of the developing roller and remains

[ Table 1]

1 polyol: manufactured by Daicel Chemical Industries, Ltd., trade name "PLACCEL 220 AL"

2 polyisocyanate: trade name "EXCELHARDENEERHX" manufactured by SUANIAN INDUSTRIAL CO., LTD "

3 carbon black a: manufactured by Yuguka pigment corporation, trade name "# 273", average particle diameter 250nm, and DBP oil absorption 810mL/100g

4 carbon black B: manufactured by Yuguka pigment corporation, trade name "# RK 034", average particle diameter 140nm, and DBP oil absorption 1100mL/100g

5 metal-containing carbamation catalyst a: dibutyl tin, trade name "U100" manufactured by Nidok chemical industries, Ltd "

6 metal-containing carbamation catalyst B: inorganic bismuth, trade name "U600" manufactured by Nidoku chemical industries Ltd "

7 metal-containing carbamation catalyst C: zirconium tetraacetylacetonate, manufactured by Matsumoto Fine Chemical co.ltd., trade name "ZC 700"

Catalyst a for amine carbamation reaction: phenolate, manufactured by San-Apro Ltd, trade name "U-CAT SA 1"

Catalyst B for amine carbamation reaction: dimethyldecylamine, product name "DM 1098" available from Kao corporation "

10 particles: fine polyurethane particles having a universal hardness of 0.43N/mm, a trade name of "Art-pearl JB 300T" manufactured by Kokusan Kogyo Co., Ltd²An average particle diameter of 22 μm and a glass transition temperature (Tg) of-52 DEG C

Comparative example 2 in table 1 is an example in which the content of carbon black in the surface layer is reduced as compared with comparative example 1, and although fog is successfully suppressed, the initial image density becomes poor, and further, toner contamination occurs.

In comparative example 3, the surface layer of comparative example 2 was added with a metal-containing urethane reaction catalyst, and although toner contamination was successfully improved, the initial image density was deteriorated.

Example 1 is an example in which carbon black having a large average particle diameter and a large DBP oil absorption was used as the carbon black contained in the surface layer, as compared with comparative example 3, and the initial image density was successfully improved while fog and toner contamination were suppressed.

In comparative examples 5 and 6, in which the urethane-forming reaction catalyst added to the surface layer was replaced with the urethane-forming reaction catalyst of the amine type containing no metal in example 1, toner contamination was not sufficiently improved, and in comparative example 5, the hardness of the surface layer was high and fog was not suppressed.

From the above results, it is understood that the developing roller according to the embodiment of the present invention can suppress fog and toner contamination while maintaining a good initial image density.

Industrial applicability

The developing roller of the present invention can be used in various image forming apparatuses of electrophotographic system such as copying machines, facsimile machines, and Laser Beam Printers (LBP).

Claims

1. A developing roller is characterized by comprising a mandrel member, an elastic layer arranged on the outer side of the mandrel member in the radial direction, and a surface layer arranged on the outer side of the elastic layer in the radial direction,

the surface layer contains a thermosetting urethane resin, carbon black, and a metal-containing urethane reaction catalyst,

2. The developer roller according to claim 1, wherein the metal-containing urethane reaction catalyst is a tin-based compound.

3. The developing roller according to claim 1 or 2, wherein the surface layer has a universal hardness of 0.4N/mm at an indentation depth of 10 μm²The following.

4. The developing roller according to claim 1 or 2, wherein the thermosetting urethane resin is obtained by further reacting a urethane prepolymer synthesized from a mixture of a polyol component and a polyisocyanate component with a polyol component and/or a polyisocyanate component,

the isocyanate index NCO/OH of a mixture of a polyol component and a polyisocyanate component used in the synthesis of the urethane prepolymer is 0.1 to 0.2.

5. The developing roller according to claim 3, wherein the thermosetting urethane resin is obtained by further reacting a urethane prepolymer synthesized from a mixture of a polyol component and a polyisocyanate component with a polyol component and/or a polyisocyanate component,