JP2008233447A - Developing roller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing roller which maintains electrification imparting performance and toner conveying performance at a fixed level even when printing many sheets by imparting durability to a covering layer, and stably forms a toner image having predetermined density and free from density irregularity. <P>SOLUTION: In the developing roller 25 constituted by forming the covering layer 12 having conductivity on the outer periphery of a conductive shaft 11, the covering layer 12 has at least inorganic oxide particles and photosetting resin. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a developing roller used for electrophotographic image formation.

  The electrophotographic image forming method widely used at present is a non-contact method in which a charged toner is brought into contact with an electrostatic latent image formed on an electrophotographic photosensitive member to make contact with the toner, or a narrow gap is made to fly. In this method, a toner image is formed on an electrophotographic photosensitive member through a developing process for visualizing the image, and the toner image is transferred to plain paper or the like and then thermally fixed to form a final image.

  As a developing method for forming a toner image, a two-component developing system in which toner is charged and developed using a two-component developer composed of a carrier and toner, or a developing roller and a developer regulating member using only toner There is a one-component development system in which development is carried out by charging with friction with the like. Since the carrier is not used in the one-component development method, the developing device can be simplified, and in recent years, it has been widely used. In particular, with the trend of colorization in recent years, a non-magnetic one-component development method using a toner that does not contain a magnetic material is attracting attention because it can be colored.

  In this method, the toner is charged by rubbing against the charging member or pressing the developing roller surface or the like, and the mechanism of the developing device (hereinafter also referred to as a developing device) is not complicated and can be made compact. There is a merit. Therefore, it can be easily applied to a color image forming apparatus that requires four or more developing devices. Particularly, in recent years, the weight reduction and downsizing of the devices have been actively promoted. Development methods using agents are the mainstream.

  As the developing roller in this non-magnetic one-component developing system, conventionally, for example, a roller in which an elastic layer using silicone rubber is formed on the outer periphery of a conductive shaft has been used. To charge the toner, a thin layer of toner is formed on the developing roller using a charging member such as a metal plate or a roller, and at the same time, the toner is rubbed against these members.

  In the developing roller, as described above, an elastic layer using a rubber-like elastic body such as silicone rubber is formed on the outer peripheral surface of a metallic or conductive resin shaft. In order to improve the surface layer, a surface layer may be formed on the elastic layer. It is known to use fluororubber for the surface layer in order to prevent toner adhesion and fusion. In order to form a fluororubber layer on the elastic layer, it is necessary to improve the adhesiveness, and an intermediate layer of a silane coupling agent is formed on the elastic layer surface, and further a fluororubber or the like as a main component is formed thereon. It is known to form by applying a coating solution (see, for example, Patent Document 1).

  In addition, as a measure to meet the needs for lighter and smaller image forming apparatuses in recent years, the development of smaller and lighter developing devices has been studied. Became to be considered. In view of this, the present inventors examined the development of a developing roller having a structure in which a coating layer is directly provided on the outer periphery of the conductive shaft in order to reduce the size and weight of the developing roller. In order to maintain and improve the charge imparting performance and toner transport performance of the developing roller, the resin constituting the coating layer has been studied.

That is, in the developing roller used in the non-magnetic one-component developing method, for example, the above-mentioned two performances are required to be stably expressed even when, for example, continuous printing of 5000 sheets or more is performed. The roller surface is required to have durability that does not wear excessively. Specifically, it is intended to improve the durability of the coating layer using a resin that forms a cross-linked structure, and by irradiating light in the presence of a cross-linking agent or other cross-linkable resin, a highly durable resin Attention was focused on the formation of a coating layer using a photocurable resin from which the above can be obtained. This was considered to be an effective resin for forming a coating layer because an acrylate resin among the photo-curable resins can be obtained as a resin having a high surface hardness. In fact, a technique for producing a developing roller using a urethane acrylate resin or an epoxy acrylate resin as a photocurable resin has been disclosed (see, for example, Patent Document 2).
JP-A-8-190263 JP 2005-17365 A

  By the way, in order to maintain stable image formation, the developing roller is required to have a capability of appropriately leaking residual charges on the roller surface to the conductive shaft in addition to the above-described charging performance and toner transport performance. That is, this is achieved by imparting some conductivity to the resin layer, and a conductive agent such as carbon black is mainly contained in the resin layer.

  However, when forming a coating layer using a photocurable resin, it became clear that irradiation light was absorbed by the presence of carbon black and a highly durable coating layer was not formed. For example, when the above-described developing roller performs continuous printing at a level exceeding 5000 sheets, the coating layer is worn and the charge imparting performance and toner transportability fluctuate, so that the image quality cannot be maintained.

  As described above, in the developing roller in which the coating layer is formed using the photocurable resin, a highly durable coating layer cannot be obtained due to the influence of carbon black. The present invention provides a highly durable developing roller in which a coating layer is not worn even when a large number of prints are made with respect to a developing roller that directly forms a coating layer on a conductive shaft using a photocurable resin. The purpose is to do.

  Specifically, by imparting durability to the coating layer, a constant level of charge imparting performance and toner transport performance are maintained even when a large number of prints are made, and the toner has a predetermined density and no density unevenness. A developing roller capable of stably producing an image is provided.

  The present invention is achieved by adopting the following configuration.

  1. A developing roller comprising a conductive coating layer formed on an outer periphery of a conductive shaft, wherein the coating layer includes at least inorganic oxide particles and a photocurable resin.

  2. 2. The developing roller as described in 1 above, wherein the inorganic oxide particles have a number average primary particle size of 5 to 150 nm.

  3. 3. The developing roller according to 1 or 2, wherein the photocurable resin is a resin formed using a monomer or elastomer having a polyfunctional acrylate group.

  According to the present invention, the durability of the coating layer directly formed on the conductive shaft is improved. For example, even when a large number of prints exceeding 5000 sheets are continuously formed, charging on the surface of the developing roller is imparted. Performance and toner transport performance are maintained at a certain level. As a result, it has become possible to stably provide a print having a predetermined toner density and a good toner image having no density unevenness.

  In order to obtain a developing roller capable of solving the above-mentioned problems, the present inventors use a conductive agent that does not inhibit the photo-curing reaction even when used in combination with a photo-curing resin, and a coating made of a photo-curable resin. The technology for forming the layer was studied.

  As a result of various studies, it has been found that when specific inorganic oxide particles are used as a conductive agent, a coating layer having sufficient hardness is formed without inhibiting the photocuring reaction. That is, it has been found that the wear resistance of the coating layer provided on the outer periphery of the conductive shaft can be improved.

  The inorganic oxide particles according to the present invention have a particle size that is small enough to transmit irradiation light for photocuring, have good dispersibility, and have sufficient conductivity.

  Moreover, it is preferable that the photocurable resin which forms a coating layer is resin formed using the monomer or elastomer which has a polyfunctional acrylate group.

  Hereinafter, the present invention will be described in detail.

  First, the configuration of the developing roller will be described.

<Configuration of developing roller>
The developing roller of the present invention is configured by forming a conductive coating layer having at least a photocurable resin and inorganic oxide particles on the outer periphery of a conductive shaft.

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

  In FIG. 1, 25 is a developing roller, 11 is a conductive shaft, 12 is a coating layer, 13 is a lower layer, and 14 is an upper layer.

  In the developing roller of the present invention, even if the coating layer 12 is directly provided on the conductive shaft 11 as shown in FIG. 1A, the lower layer 13 is provided on the conductive shaft 11 as shown in FIG. Alternatively, the cover layer 12 having a multilayer structure in which the upper layer 13 is provided may be used. Each of the lower layer and the upper layer may be formed of a plurality of layers.

  Next, materials and manufacturing methods used for manufacturing the developing roller will be described.

《Conductive shaft》
Since the conductive shaft used in the present invention also serves as a member that leaks charges accumulated on the surface of the developing roller, it is preferable that the conductive shaft is made of a conductive metal. Typical examples include conductive metals such as stainless steel (for example, SUS303) having a diameter of 5 to 30 mm, iron, aluminum, nickel, an aluminum alloy, and a nickel alloy, and may be made of a conductive resin.

<Coating layer>
The coating layer according to the present invention comprises a photocurable resin component (monomer or elastomer), inorganic oxide particles, and optionally various additives such as an ionic conductive agent, a nonconductive filler (roughness particles), and a crosslinking agent. The coating liquid obtained by appropriately blending the above can be applied to the outer peripheral surface of the conductive shaft, dried to form a film, and then irradiated with light to cure the photocurable resin component.

<Photocurable resin component>
The photocurable resin referred to in the present invention refers to a resin obtained by curing a photochemical reaction of a monomer or elastomer that is a photocurable resin component by irradiation with light.

  The monomer or elastomer used as the photocurable resin component is not particularly limited as long as it is cured by light irradiation, but an acrylic having a polyfunctional group that easily forms a crosslinked structure and easily forms a resin having a high surface hardness. Preferred are monomers or elastomers of the system.

  Specific examples of the photo-curing acrylic resin include a cured (meth) acrylic resin, and the coating layer of the cured (meth) acrylic resin includes, for example, a (meth) acrylic monomer or oligomer and a polymerization initiator. After forming the coating film to contain, it can obtain by irradiating with an ultraviolet-ray.

The cured acrylic monomer or oligomer is a compound having a plurality of acryloyloxy groups (CH ₂ ═CHCOO—) or methacryloyloxy groups (CH ₂ ═C (CH ₃ ) COO—).

  If the example of a typical compound is given, the thing of the following structure can be mentioned.

  Examples of the polymerization initiator used for the photocuring reaction include benzophenone, Michler ketone, 1-hydroxycyclohexyl-phenyl ketone, thioxanthone, benzobutyl ether, acyloxime ester, dibenzothroben, bisacylphosphine oxide, and the like.

  The hardness characteristics of the coating layer are affected by the type of photocuring acrylic monomer or oligomer, its composition ratio, photocuring conditions, and the like.

  That is, the coating layer is preferably a resin prepared by reacting a monomer (polyfunctional monomer) having a bifunctional or higher functional group with a cured (meth) acrylic resin to be formed. Mainly a resin formed by reacting a monomer having a group and a cured (meth) acrylic acid having an alkyl group having 12 or more carbon atoms, or a resin formed by reacting with a bifunctional oligomer It is particularly preferable that it is contained as a component.

  The coating layer may be formed by adding a known resin to the above-described photocurable resin.

<Inorganic oxide particles>
The inorganic oxide particles according to the present invention preferably have a form that transmits without irradiating the irradiation light used for the photocuring reaction.

  The inorganic oxide particles preferably have a number average primary particle size of 5 to 150 nm, more preferably 10 to 100 nm.

The inorganic oxide particles preferably function as a conductive agent in the coating layer, and specifically those having a volume resistance of 1 to 1 × 10 ¹⁰ Ω · cm are preferable.

  The content of the inorganic oxide particles is preferably 5 to 50% by mass and more preferably 10 to 30% by mass in the coating layer.

  The inorganic oxide particles have good dispersion stability in the coating layer coating solution, transmit light irradiated during photocuring, and allow the photocurable resin component to be uniformly photocured. Since the coating layer formed using this coating solution has a high hardness and a uniform hardness, image defects (black spots, white spots) do not occur in the halftone image area even when a large number of sheets are printed. A high-quality toner image can be obtained.

  The number average primary particle size of the inorganic oxide particles is magnified 10,000 times on the surface of the coating layer by transmission electron microscope observation, 100 particles are randomly observed as primary particles, and the average of the ferret direction is determined by image analysis. It is a measured value as a diameter.

  Examples of the inorganic oxide particles used in the present invention include titanium oxide, zinc oxide, cerium oxide, ferric oxide, magnesium oxide, tin oxide, zirconium oxide, and antimony oxide.

  Among these, titanium oxide, zinc oxide, tin oxide, and antimony oxide are preferable. These particles suppress the injection of carriers from the conductive shaft and are excellent in the effect of preventing black spots.

  In addition, the inorganic oxide particles may be particles containing one or more of these as required. Further, those obtained by treating the surface of these particles in order to achieve good dispersibility can also be used.

<Ionic conductive agent>
As the ionic conductive agent, conventionally known inorganic ionic salts and organic ionic salts can be appropriately selected and used. Specifically, alkali metal halides such as Li, LiCl, NaI, NaBr, and KI, perchlorates such as LiClO ₄ , KClO ₄ , and CuC ₁₂ Mg (ClO ₄ ) ₂ , and thiocyanic acids such as LiSCN, NaSCN, and CsSCN Inorganic ion salts such as salts, aliphatic sulfonates, higher alcohol sulfates, higher alcohol phosphates, higher alcohol ethylene oxide addition sulfates, higher alcohol ethylene oxide addition phosphates, quaternary ammonium Examples thereof include organic ion salts such as salts and betaines. Among these, quaternary ammonium salts such as trimethyloctadecyl ammonium perchlorate, tetramethylammonium chloride, and benzyltrimethylammonium chloride are particularly preferable. These ionic conductive agents may be used alone or in combination of two or more.

  The compounding amount of the ionic conductive agent is not particularly limited and is appropriately selected according to various situations, but is preferably 0.001 to 5 parts by mass with respect to 100 parts by mass of the resin component forming the coating layer, and 0.05 to 2 Part by mass is more preferable.

<Non-conductive filler (roughness particles)>
Examples of the non-conductive filler include diatomaceous earth, quartz powder, dry silica, wet silica, titanium oxide, zinc oxide, aluminosilicate, calcium carbonate, and resin particles. Among these, resin particles are preferable, and as the resin particles, crosslinked acrylic resin particles and crosslinked urethane resin particles are particularly preferable.

<Production of developing roller>
The developing roller of the present invention forms a conductive coating layer having at least a photocurable resin and inorganic oxide particles on the outer periphery of the conductive shaft, and then irradiates ultraviolet rays to perform a photocuring reaction. Can be made by curing.

  As a means for forming a coating layer on the outer peripheral surface of the conductive shaft, a means for applying a coating solution prepared by dissolving and dispersing the material forming the coating layer in an organic solvent onto the conductive shaft is effectively employed. . The resin component concentration of the coating solution is not particularly limited and may be appropriately adjusted according to the required layer thickness. However, the resin component concentration is 10% by mass or more from the dispersibility and stability of various additives in the coating solution. It is preferable that The solvent used for preparing the coating solution may be any solvent as long as it can dissolve the resin component, for example, lower alcohols such as methanol, ethanol and isopropanol, ketones such as methyl ethyl ketone, cyclohexane, Toluene, xylene and the like are preferably used.

  Examples of the means for forming the coating layer include dip coating, spray coating, roll coating, brush coating, and the like depending on the viscosity of the resin component constituting the resin layer, and the present invention particularly limits this forming means. It is not a thing.

  The light source for light irradiation is not particularly limited as long as the photocurable resin can be cured. For example, a mercury lamp or a xenon lamp that emits ultraviolet rays can be used.

  In order to uniformly cure the coating layer, the light irradiation is preferably performed while rotating the developing roller on which the coating layer is formed.

  The thickness of the coating layer thus formed is preferably set in the range of 2 to 30 μm, more preferably 5 to 20 μm.

  The thickness of the coating layer can be measured from a micrograph of the cross-sectional sample obtained by taking a cross-sectional sample including the coating layer from the developing roller.

The hardness of the coating layer is preferably 50 to 400 N · mm ² in terms of universal hardness (HU), and more preferably 300 to 400 N · mm ² . By setting the hardness of the coating layer within the above range, wear of the coating layer due to printing can be reduced.

  The universal hardness can be measured using a commercially available hardness measuring device. For example, an ultra-micro hardness meter “H-100V” (manufactured by Fisher Instrument Co.) is used and measured under the following measurement conditions. be able to.

Measurement conditions Measuring machine: micro hardness tester "H-100V" (Fischer Instrument Co., Ltd.)
Indenter shape: Vickers indenter (a = 136 °)
Measurement environment: 20 ° C, 60% RH
Maximum test load: 3mN
Load speed: 3mN / 20sec
Maximum load creep time: 5 seconds Unloading speed: 3mN / 20sec
In addition, each sample was measured at a total of 15 points including 5 points at equal intervals in the axial direction and 3 points at equal angles in the circumferential direction, and the average value is universal hardness (HU) (N / mm) defined in the present invention. ² ).

  The conductivity of the coating layer can be evaluated by volume resistivity. As a method for measuring the volume resistivity, it can be measured by a known method.

In the present invention, when the volume resistivity of the developing roller measured by the following method is 1 × 10 ² to 1 × 10 ⁹ Ω · cm, it is determined that the conductive roller exhibits appropriate conductivity. Particularly preferably, it is 1 × 10 ³ to 1 × 10 ⁸ Ω · cm. This is because, when the volume resistivity of the developing roller is in the above range, the charge generated on the surface of the developing roller leaks moderately and the leak is moderately suppressed.

  The volume resistivity of the developing roller can be typically measured by a metal roller electrode method using an apparatus as shown in FIG.

  FIG. 2 is a configuration diagram illustrating the volume resistivity of the developing roller.

  In FIG. 2, the electrode roller 101 made of stainless steel is brought into contact with the developing roller 25 and is pressed with 9.8 N together with the weight of the electrode roller 101. While rotating the roller in this state, + 100V is applied to one end of the developing roller 25. Apply voltage and measure current. From the measured current value, the following formula (1) is used to obtain the volume resistivity of the developing roller by calculation.

Formula (1)
R = V / I
Measurement conditions Measurement environment: 23 ° C, 57RH%
Applied voltage: + 100V
Roller rotation speed: 27rpm
Electrode roller load: 9.8 N (including electrode roller weight)
Effective width of electrode roller: 230 mm (diameter 30 mm)
Measurement item: Current value (average value after 5 seconds of voltage application)
The non-magnetic one-component developer in the present invention refers to a heat-fixable toner that does not contain a magnetic material in the toner and can be used as a developer only with toner without using a carrier.

The median diameter (D ₅₀ ) on the volume basis of the toner is preferably 3 to 9 μm from the viewpoint of obtaining a high-quality toner image.

  Specific examples of the resin constituting the toner include a polyester resin and an acrylic resin.

  The method for producing the toner is not particularly limited, and the toner can be produced by a known polymerization method or pulverization method.

  Next, the developing device and the full-color image forming apparatus according to the present invention will be described.

  FIG. 3 is a schematic sectional view showing an example of the developing device according to the present invention.

  The developing device 20 shown in FIG. 3 has a buffer chamber 26 adjacent to the developing roller 25, and a hopper 27 and the like adjacent to the buffer chamber 26.

  In the buffer chamber 26, a blade 28 as a toner regulating member is disposed in pressure contact with the developing roller 25. The blade 28 regulates the charge amount and adhesion amount of the toner on the developing roller 25. Further, it is possible to further provide an auxiliary blade 29 for assisting regulation of the toner charge amount and adhesion amount on the developing roller 25 on the downstream side of the blade 28 with respect to the rotation direction of the developing roller 25.

  A supply roller 30 is pressed against the developing roller 25. The supply roller 30 is driven to rotate in the same direction as the developing roller 25 (counterclockwise direction in the drawing) by a motor (not shown). The supply roller 30 has a conductive cylindrical base and a foam layer formed of urethane foam or the like on the outer periphery of the base.

  The hopper 27 contains toner T which is a non-magnetic one-component developer. The hopper 27 is provided with a rotating body 31 for stirring the toner T. A film-like conveying blade is attached to the rotating body 31, and the toner T is conveyed by the rotation of the rotating body 31 in the arrow direction. The toner T conveyed by the conveying blades is supplied to the buffer chamber 26 via a passage 28 provided in a partition wall that separates the hopper 27 and the buffer chamber 26. The shape of the conveying blade is bent while conveying the toner T in front of the rotating direction of the blade as the rotating body 31 rotates, and returns to a straight state when the left end of the passage 32 is reached. Thus, the toner T is supplied to the passage 32 by returning the shape of the blade straightly through the curved state.

  The passage 32 is provided with a valve 321 for closing the passage 32. This valve is a film-like member, and one end is fixed to the upper side of the right side of the passage 32 of the partition wall. When the toner T is supplied from the hopper 27 to the passage 28, the valve 32 is pushed rightward by the pressing force from the toner T. Can be opened. As a result, the toner T is supplied into the buffer chamber 26.

  A restricting member 322 is attached to the other end of the valve 321. The regulating member 322 and the supply roller 30 are arranged so as to form a slight gap even when the valve 321 closes the passage 32. The regulating member 322 adjusts so that the amount of toner accumulated at the bottom of the buffer chamber 26 does not become excessive, so that a large amount of toner T collected from the developing roller 25 to the supply roller 30 does not fall to the bottom of the buffer chamber 26. Adjusted to

  In the developing device 20, the developing roller 25 is rotationally driven in the arrow direction during image formation, and the toner in the buffer chamber 26 is supplied onto the developing roller 25 by the rotation of the supply roller 30. The toner T supplied onto the developing roller 25 is charged and thinned by a blade 28 and an auxiliary blade 29, and then conveyed to a region facing the photosensitive drum to develop an electrostatic latent image on the photosensitive drum. To be served. The toner that has not been used for development returns to the buffer chamber 26 as the developing roller 25 rotates, and is scraped and collected from the developing roller 25 by the supply roller 30.

  FIG. 4 is a schematic sectional view showing an example of a full-color image forming apparatus.

  In the full-color image forming apparatus shown in FIG. 4, a charging brush 111 that uniformly charges the surface of the photosensitive drum 10 to a predetermined potential around the photosensitive drum 10 that is rotationally driven, and the photosensitive drum 10 A cleaner 112 for scraping off the remaining toner is provided.

  Further, a laser scanning optical system 20 for scanning and exposing the photosensitive drum 10 charged by the charging brush 111 with a laser beam is provided. The laser scanning optical system 20 includes a laser diode, a polygon mirror, and an fθ optical element. As is well known, print data for each of yellow, magenta, cyan, and black is transferred from the host computer to the control unit. The laser scanning optical system 20 sequentially outputs the laser beam as a laser beam based on the print data for each color, scans and exposes the photosensitive drum 10, and thereby the static image for each color is formed on the photosensitive drum 10. Electro latent images are sequentially formed.

  In addition, the full-color developing device 30 that supplies full-color development to the photosensitive drum 10 on which the electrostatic latent image is formed in this manner, performs yellow, magenta, cyan, and black around the support shaft 33. Four color-developing units 31Y, 31M, 31C, and 31Bk each containing non-magnetic one-component toner are provided. The developing units 31Y, 31M, 31C, and 31Bk rotate around the support shaft 33, and the developing units 31Y, 31M, 31C, and 31Bk are rotated. It is guided to a position facing the photosensitive drum 10.

  Further, in each of the developing devices 31Y, 31M, 31C, and 31Bk in the full color developing device 30, a toner regulating member is pressed against the outer peripheral surface of the developing roller 25 that rotates and conveys the toner, as shown in FIG. The toner regulating member regulates the amount of toner conveyed by the developing roller 25 and charges the conveyed toner. In the full-color developing device 30, two toner regulating members may be provided in order to appropriately regulate and charge the toner conveyed by the developing roller.

  Then, whenever the electrostatic latent image of each color is formed on the photosensitive drum 10 by the laser scanning optical system 20 as described above, the full-color developing device 30 is rotated around the support shaft 33 as described above. Then, the developing devices 31Y, 31M, 31C, and 31Bk containing toner of the corresponding colors are sequentially guided to positions facing the photosensitive drum 10, and the developing rollers 25 in the developing devices 31Y, 31M, 31C, and 31Bk are moved. Development is performed by sequentially supplying charged toner of each color onto the photosensitive drum 10 in which the electrostatic latent images of each color are sequentially formed as described above in contact with the photosensitive drum 10. It has become.

  Further, an endless intermediate transfer belt 40 that is rotationally driven is provided as an intermediate transfer body 40 at a position downstream of the full-color developing device 30 in the rotation direction of the photosensitive drum 10. Is driven to rotate in synchronization with the photosensitive drum 10. The intermediate transfer belt 40 is pressed by a rotatable primary transfer roller 41 so as to come into contact with the photosensitive drum 10, and a portion of a support roller 42 that supports the intermediate transfer belt 40 includes: A secondary transfer roller 43 is rotatably provided, and the recording material S such as recording paper is pressed against the intermediate transfer belt 40 by the secondary transfer roller 43.

  Further, a cleaner 50 that scrapes off the toner remaining on the intermediate transfer belt 40 is provided in a space between the full-color developing device 30 and the intermediate transfer belt 40 so as to be able to contact with and separate from the intermediate transfer belt 40. ing.

  Further, the paper feeding means 60 that guides the recording material S such as plain paper to the intermediate transfer belt 40 includes a paper feeding tray 61 that accommodates the recording material S and the recording material S that is accommodated in the paper feeding tray 61 one by one. The recording material S fed in synchronization with the paper feed roller 62 for feeding paper and the image formed on the intermediate transfer belt 40 is sent between the intermediate transfer belt 40 and the secondary transfer roller 43. The recording material S sent between the intermediate transfer belt 40 and the secondary transfer roller 43 in this way is pressed against the intermediate transfer belt 40 by the secondary transfer roller 43. The toner image is pressed and transferred from the intermediate transfer belt 40 to the recording material S.

  On the other hand, the recording material S on which the toner image is pressed and transferred as described above is guided to the fixing device 70 by the conveying means 66 constituted by an air suction belt or the like, and is transferred by the fixing device 70. The toner image is fixed on the recording material S, and then the recording material S is discharged onto the upper surface of the apparatus main body 100 through the vertical conveyance path 80.

  Next, the operation of forming a full color image using this full color image forming apparatus will be specifically described.

  First, the photosensitive drum 10 and the intermediate transfer belt 40 are rotationally driven in the respective directions at the same peripheral speed, and the photosensitive drum 10 is charged to a predetermined potential by the charging brush 11.

  The photosensitive drum 10 thus charged is exposed to a yellow image by the laser scanning optical system 20 to form an electrostatic latent image of a cyan image on the photosensitive drum 10. The yellow image is developed by supplying the yellow toner charged by the toner regulating member as described above from the developing device 31Y in which the yellow toner is accommodated in the photosensitive drum 10, and the yellow toner image is thus formed. The intermediate transfer belt 40 is pressed against the body drum 10 by the primary transfer roller 41, and the yellow toner image formed on the photosensitive drum 10 is primarily transferred to the intermediate transfer belt 40.

  After the yellow toner image is transferred to the intermediate transfer belt 40 in this way, the full-color developing device 30 is rotated around the support shaft 33 as described above, and the developing device 31M containing magenta toner is exposed to light. As in the case of the yellow image described above, the magenta image is exposed to the photosensitive drum 10 charged by the laser scanning optical system 20 to form an electrostatic latent image. The electrostatic latent image is developed by a developing device 31M containing magenta toner, and the developed magenta toner image is primarily transferred from the photosensitive drum 10 to the intermediate transfer belt 40. Black image exposure, development and primary transfer are sequentially performed, and yellow, magenta, cyan, and black toner images are sequentially superimposed on the intermediate transfer belt 40. To form a toner image of Rukara.

  When the final black toner image is primarily transferred onto the intermediate transfer belt 40, the recording material S is fed between the secondary transfer roller 43 and the intermediate transfer belt 40 by the timing roller 63, and the secondary transfer roller. The recording material S is pressed against the intermediate transfer belt 40 by 43, and the full color toner image formed on the intermediate transfer belt 40 is secondarily transferred onto the recording material S.

  When the full-color toner image is secondarily transferred onto the recording material S in this way, the recording material S is guided to the fixing device 70 by the conveying means 66, and the full-color toner transferred by the fixing device 70 is transferred. The image is fixed on the recording material S, and then the recording material S is discharged onto the upper surface of the apparatus main body 1 through the vertical conveyance path 80.

  The present invention will be specifically described below with reference to examples, but the embodiments of the present invention are not limited to these examples.

<Production of developing roller>
A developing roller was produced as follows.

(Preparation of conductive shaft)
As a developing roller shaft, a hollow cylindrical conductive shaft of SUS303 was prepared. This is referred to as “shaft 1”.

<Preparation of developing roller 1>
(Preparation of coating layer forming coating solution 1)
The following coating layer coating composition was dispersed using a sand mill for 2 hours to prepare a coating layer forming coating solution. This is designated “Coating Layer Forming Coating Solution 1”.

Coating composition for coating layer Acrylic monomer “KAYARAD DPHA” (manufactured by Nippon Kayaku Co., Ltd.) 100 parts by mass Polymerization initiator “Irgacure 184” (manufactured by Ciba Specialty Chemicals)
5 parts by mass Inorganic oxide particles (ZnO / Sb ₂ O ₅ ) * 1 20 parts by mass Roughness particles “crosslinked acrylic resin particles”
(Median diameter (D ₅₀ ) based on volume) 15 μm 20 parts by mass Methyl ethyl ketone 200 parts by mass Isopropanol 200 parts by mass * 1: “Selnax CX-Z210IP” (solid content concentration 20% by mass: manufactured by Nissan Chemical Co., Ltd.)
(Coating layer formation)
The “coating layer forming coating solution 1” produced above was dip-coated on the “shaft 1”, and then primary dried in an oven at 30 ° C. for 30 minutes to form a coating layer. Then, while rotating the conductive shaft on which the coating layer is formed, curing is performed by irradiating an integrated light amount of 2000 mJ / cm ² from a mercury lamp with an ultraviolet intensity of 1 kW / cm ^2. 1 "was formed, and" Developing roller 1 "was produced.

<Developing rollers 2-5>
“Developing rollers 2 to 5” were produced in the same manner except that the types of inorganic oxide particles (ZnO / Sb ₂ O ₅ ) used in the production of the developing roller 1 and the addition amount thereof were changed as shown in Table 1. .

<Developing roller 6>
“Developing roller 6” was produced in the same manner except that the inorganic oxide particles used in the production of developing roller 1 were not added.

<Developing roller 7>
(Preparation of coating layer forming coating solution 7)
In a solution obtained by dissolving 100 parts by mass of thermoplastic acrylic resin “Acrylic 1: Sumipex LG” (manufactured by Sumitomo Chemical Co., Ltd.) in 700 parts by mass of methyl ethyl ketone, 40 parts by mass of inorganic oxide particles (ZnO / Sb ₂ O ₅ ), benzyltrimethyl A coating solution for forming a coating layer was prepared by dispersing 5.0 parts by mass of ammonium chloride and 30 parts by mass of a crosslinked acrylic resin particle having a median diameter (D ₅₀ ) of 15 μm on a volume basis using a sand mill for 2 hours. This is designated as “Coating Layer Forming Coating Liquid 7”.

(Coating layer formation)
“Coating layer forming coating solution 7” is dip coated on the outer peripheral surface of “Shaft 1” and then dried at 120 ° C. for 1 hour to form a coating layer having a dried film thickness of 10 μm. Was made.

  Table 1 shows the universal hardness (HU) of the inorganic oxide particles (types and their number average primary particle diameter and addition amount) and resin used for developing roller development, and the coating layer after photocuring.

<Evaluation>
<Universal hardness (HU) of the coating layer after photocuring>
The universal hardness (HU) of the coating layer after photocuring is a value obtained by measurement by the above method.

<Live-action evaluation>
The evaluation of the actual condition of the developing roller was carried out by sequentially mounting the developing roller prepared above on a color laser printer “Magicor2430DL” (manufactured by Konica Minolta Business Technologies), normal temperature and humidity (20 ° C., 55% RH), and high temperature and high humidity. 5000 sheets were printed in an environment (33 ° C., 80% RH).

  The initial performance evaluation of the developing roller was performed by printing 10 A4-size originals with a pixel rate of 20% (full color mode of 5% for each color of yellow, magenta, cyan, and black), and using the toner image quality and the residual potential of the developing roller. evaluated.

  Thereafter, 5000 sheets were printed using a document having an image rate of 2% (full color mode of 0.5% for each color of yellow, magenta, cyan, and black).

  The performance evaluation after printing 5000 sheets was done by printing 10 A4 size originals with the same pixel ratio 20% (5% each color of yellow, magenta, cyan and black) as the initial performance evaluation, and the toner image quality ( Image density, halftone image) and abrasion (occurrence of scratches) were evaluated.

(Abrasion)
Abrasion was evaluated based on the state of scratches caused by abrasion. Specifically, after the completion of printing 5000 sheets in a high temperature and high humidity environment (33 ° C., 80% RH), the state of occurrence of scratches on the surface of the developing roller was evaluated from images obtained by visual observation and printing.

Evaluation criteria A: No visible scratches ○: There are two visible scratches, but they do not appear in the printed image ×: There are three or more visible scratches, and appear as image defects in the printed image.

(Image density)
As for the image density, a reflection densitometer “RD-918” (manufactured by Macbeth Co., Ltd.) was used to measure the density of the solid black image portion after printing at normal temperature and humidity (20 ° C., 55% RH) and after printing 5000 sheets. 12 points were measured and evaluated.

Evaluation criteria A: The density of the solid black image portion is excellent when it is 1.40 or more. ○: The density of the solid black image portion is 1.20 or more and less than 1.40. Concentration is less than 1.20 and is a practical problem.

(Density unevenness of halftone images (including black spots and white spots))
The density unevenness of the halftone image was evaluated by visually observing a print at the completion of 50 million prints printed in a normal temperature and normal humidity environment (20 ° C., 55% RH).

Evaluation Criteria A: Uniform image without density unevenness in the halftone part ○: There are streaky thin density unevenness, black spots, and white spots in the halftone part, but there is no practical problem ×: In the halftone part There are several streaky density irregularities, black spots, and white spots, which is a practical problem.

  Table 2 shows the evaluation results.

  As shown in Table 2, the “developing rollers 1 to 4” of Examples 1 to 4 corresponding to the present invention had a hard coating layer after photocuring, and good wear resistance, image density, and halftone image unevenness. On the other hand, the “developing rollers 5 to 7” of Comparative Examples 1 to 3 outside the present invention were not cured or soft after photocuring, and there was a problem with any of the evaluation items. It was confirmed that the effects of the invention were not expressed.

It is a cross-sectional schematic diagram showing an example of the developing roller of the present invention. It is a block diagram explaining the volume resistivity of a developing roller. FIG. 3 is a schematic cross-sectional view showing an example of a developing device to which the developing roller of the present invention is attached and used. 1 is a schematic cross-sectional view illustrating an example of a full-color image forming apparatus.

Explanation of symbols

25 Developing roller 11 Conductive shaft 12 Coating layer 13 Lower layer 14 Upper layer

Claims (3)

A developing roller comprising a conductive coating layer formed on an outer periphery of a conductive shaft, wherein the coating layer includes at least inorganic oxide particles and a photocurable resin. The developing roller according to claim 1, wherein the inorganic oxide particles have a number average primary particle size of 5 to 150 nm. The developing roller according to claim 1, wherein the photocurable resin is a resin formed using a monomer or elastomer having a polyfunctional acrylate group.

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