JP5253022B2 - Development device - Google Patents

Description

  The present invention relates to a developing device having a function of forming an image on a recording material such as a sheet and applied to an image forming apparatus such as a copying machine or a printer.

  Conventional development methods using one-component toner include a contact development method and a non-contact development method, and a developing roller is widely used as a developer carrier used at that time.

  On the developer carrying member, a developer regulating member that contacts the developer carrying member is provided for the purpose of coating regulation of the developer and charging by friction.

  As the developer regulating member, a cantilever type plate-shaped regulating blade is generally used.

  A developing roller as a developer carrying member is formed of a cored bar and an elastic body.

According to Patent Document 1, the elastic body is formed of a base layer made of conductive silicone rubber and a thin film resin surface layer made of amide resin or urethane resin having conductivity. The conductivity of the resin surface layer is obtained by dispersing carbon black. The volume resistance value of the developing roller is preferably 10 ⁴ Ω · cm or more and 10 ⁹ Ω · cm or less.

This is considered due to the following reasons. In order to obtain an effective developing potential on the surface of the developing roller with respect to the latent image potential on the latent image carrier, a volume resistance value of 10 ⁹ Ω · cm or less is required. On the other hand, in the surface layer of the latent image carrier, a volume resistance value of 10 ⁴ Ω · cm or more is required to prevent the occurrence of surge current caused by pinholes that may be rarely present due to coating unevenness or the like. is necessary.

  The problem of the surge current may be exposed to a severe situation in a high humidity environment or a deteriorated state of the latent image carrier. On the other hand, even for developing rollers having the same volume resistance, for example, it is effective to prevent the occurrence of surge current by making the resistance value of the resin surface layer higher than the resistance value of the base layer.

  On the other hand, in the regulation blade, it has been proposed for a long time to use a so-called blade bias, in which a bias is applied to the developer carrier. As the effect of the bias application, charge control on the developer on the developer carrying member, control of the developer coating amount, and the like are known.

In a developing system using a blade bias, since it is necessary to provide a potential difference between the surface of the developer carrying member and the surface of the regulating blade, it is common to use a conductive member as the regulating blade. It was.
JP 2001-323160 A

However, for example, when a metal is used as the regulating blade, the following cautions are necessary. That is, the only thing that maintains the potential difference between the regulating blade and the developer carrying member is the surface layer of the developer carrying member in addition to the intervening toner layer, so that dielectric breakdown does not occur on the surface of the developing roller. It was necessary to pay attention to the applied bias value and the resistance value of the developing roller.

  In preventing the breakdown, the same means as preventing surge current in the pinhole of the latent image carrier is effective. However, since the regulation blade is electrically conductive on the entire surface against pinholes on the latent image carrier that are rarely present, the pressure resistance of the surface layer of the developing roller as a surge current prevention needs to be more severe. It was.

In the case of a developing roller having a volume resistance value as shown in Patent Document 1, it is considered that the volume resistance value of the surface layer is preferably in the range of about 10 ⁶ Ω · cm to 10 ⁹ Ω · cm. However, the resistance value in this range is very sensitive to conditions such as the dispersibility of the conductive material, and it is difficult to stably obtain a desired resistance value.

  In addition, since the layer thickness is thin, there is a concern that the influence of the dispersibility of the conductive material becomes larger, for example, when the conductive material is localized even in a part of the layer, the resistance fluctuation of the portion increases.

  In addition, the electrical resistance of the thin film does not necessarily follow Ohm's law, and the electrical resistance tends to decrease as the applied voltage increases. This is because when a voltage is applied to a thin film made of a material having a relatively high resistance, a leakage current is generated. This leakage current is a phenomenon that is peculiar when the film is thin, and as the voltage increases. The current increases greatly.

  Therefore, it is very difficult to handle the resistance value of the thin film layer, and the resistance value may greatly change due to the change of the material and the fluctuation of the layer thickness, and the pressure resistance as the surface layer film or when the blade bias is applied It has been difficult to clearly grasp the relationship between the effect and the applied bias value.

  The present invention has been made in view of the above circumstances, and prevents the occurrence of abnormal images due to a bias applied between the developer carrier and the regulating member, and increases the coating amount of the developer layer on the developer carrier. The purpose of this is to expand the bias application region where a good image can be obtained.

In order to achieve the above object, the present invention provides:
A developer carrier provided rotatably with a base layer having conductivity and elasticity, and a surface layer provided on an outer peripheral side of the base layer;
A regulating member that has conductivity and is provided so as to contact the developer carrier, and that regulates one-component developer on the developer carrier;
A potential difference setting means for generating a potential difference between the developer carrier and the regulating member;
In a developing device comprising:
The developer carrying member is formed between the developer carrying member and the metal roller while rotating the developer carrying member with the metal roller being in contact with the developer carrying member so as to be driven to rotate. When bias application is performed so that the current density of the current flowing between them is 0.5 μA / mm ² or more in a stable state,
Assuming that current values after 2 seconds and 60 seconds after the bias application are respectively It and Is, and Log indicates a common logarithm,
Log (It / Is)> 0.1
Satisfying,
When the potential difference is Vb (V) and the thickness of the surface layer of the developer carrier is t (μm),
0.05 <t <4.00,
In the case of 0.05 <t ≦ 2.00, 55 × t <Vb <120 × t + 250
In the case of 2.00 <t <4.00, 55 × t <Vb <500
Meet the,
The surface layer of the developer carrier is formed of silicon oxide containing carbon atoms,
The composition ratio of oxygen and silicon (O / Si) and the composition ratio of carbon and silicon (C / Si) in the surface layer are as follows:
1.00 ≦ (O / Si) ≦ 1.95
0.05 ≦ (C / Si) ≦ 1.00
A meet and wherein the Succoth.

  According to the present invention, both the prevention of abnormal image generation due to a bias applied between the developer carrier and the regulating member and the increase in the coating amount of the developer layer on the developer carrier are achieved, and a good image is obtained. It is possible to expand the bias application region in which the above is obtained.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

  A laser printer will be described below as an example of an image forming apparatus to which the present invention can be applied.

<Image forming apparatus>
FIG. 2 is a cross-sectional view illustrating a schematic configuration of the image forming apparatus A of the present embodiment.

  The image forming apparatus A is a full color laser printer using an electrophotographic process. The image forming apparatus A includes a charging device, a developing device, a cleaning device, and a process cartridge B integrally including a photosensitive drum 1 as an image carrier (latent image carrier, developer carrier). It is detachably provided on the forming apparatus main body.

  The process cartridge B is provided with process cartridges By, Bm, Bc, and Bk corresponding to the colors yellow, magenta, cyan, and black, and these process cartridges B are arranged in parallel in one direction (four stations). Are listed).

  In the process cartridge B of each color, the developer image (toner image) formed on the photosensitive drum is transferred onto the intermediate transfer belt 20 of the transfer device, whereby a full color image is formed, and then to the recording material thereafter. An image is formed through the transfer process and the fixing process.

  Here, the electrophotographic process in this embodiment is an application of a contact developing device, and the developer used a non-magnetic one-component toner having an average particle diameter of 6.0 μm as a one-component developer for each color. . Details of the process cartridge B will be described later.

  The toner images formed on the photosensitive drums of the respective colors by the process cartridges B of the respective colors are intermediated by the primary transfer rollers 22 provided at positions facing the photosensitive drums of the respective colors with the intermediate transfer belt 20 interposed therebetween. The image is transferred onto the transfer belt 20. Here, primary transfer rollers 22y, 22m, 22c, and 22k are respectively provided at positions facing the photosensitive drums 1y, 1m, 1c, and 1k of the respective colors. The toner images transferred onto the intermediate transfer belt 20 are collectively transferred onto the recording material by the secondary transfer roller 23 provided on the downstream side in the moving direction of the intermediate transfer belt 20. The untransferred toner on the intermediate transfer belt 20 is collected by the intermediate transfer belt cleaner 21.

  The recording material P is stacked in a cassette 24 below the image forming apparatus A, and is conveyed by a feeding roller 25 together with a request for a printing operation, and a toner image formed on an intermediate transfer belt at a secondary transfer roller position. Is transcribed.

  Thereafter, the toner image on the recording material is heated and fixed on the recording material by the fixing unit 26 and is discharged to the outside of the image forming apparatus through the discharge unit 27.

  In the image forming apparatus A, an upper unit that accommodates process cartridges of four colors and the lower unit that accommodates transfer units, recording materials, and the like are separable. Then, when jam processing such as recording material clogging occurs or when a process cartridge is replaced, the above processing is performed by opening the upper and lower units.

  Next, the configuration of the process cartridge B will be described.

  FIG. 3 is a cross-sectional view showing a schematic configuration of one of the four process cartridges arranged in parallel in the image forming apparatus of the present embodiment. The configuration of the four process cartridges is essentially the same.

  In this embodiment, as the photosensitive drum 1 which is the center of the image forming process, an organic photosensitive drum in which an outer peripheral surface, a carrier generation layer, and a carrier transfer layer, which are functional films, are sequentially coated on the outer peripheral surface of an aluminum cylinder. Used. In the image forming process, the photosensitive drum 1 is driven in the direction of arrow a in the figure by the image forming apparatus at a predetermined speed.

  The charging roller 2 constituting the charging device is provided so that the roller portion of the conductive rubber is brought into pressure contact with the photosensitive drum 1, and is driven to rotate in the direction of arrow b. Here, a direct current voltage of −1100 V is applied to the cored bar of the charging roller 2 with respect to the photosensitive drum 1 as a charging process, and the surface potential of the photosensitive drum due to the charge induced thereby is A uniform dark potential (Vd) of −550 V is formed.

  The spot pattern of the laser light emitted by the scanner unit 10 corresponding to the image data is exposed to the uniform surface charge distribution surface as shown by the arrow L in FIG. To do. Then, the surface of the exposed portion is lost due to carriers from the carrier generation layer, and the potential is lowered. As a result, an electrostatic latent image is formed on the photosensitive drum with the bright portion potential Vl = −100 V at the exposed portion and the dark portion potential Vd = −550 V at the unexposed portion.

  The electrostatic latent image is developed in the developing device D by a toner coat layer formed so as to have a predetermined coating amount and charge amount, and the electrostatic latent image is converted into a real image.

  The intermediate transfer belt 20 in contact with the photosensitive drum 1 of each process cartridge B is pressed against the photosensitive drum 1 by a primary transfer roller 22 facing the photosensitive drum 1. Further, a DC voltage is applied to the primary transfer roller 22, and an electric field is formed between the primary transfer roller 22 and the photosensitive drum 1.

  As a result, the toner image formed on the photosensitive drum 1 is transferred from the photosensitive drum 1 to the intermediate transfer belt 20 under the force of an electric field in a transfer region where the intermediate transfer belt 20 is in pressure contact. The

  On the other hand, the untransferred toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 20 is scraped off from the drum surface by the urethane rubber cleaning blade 6 installed in the cleaning device C, and is stored in the cleaning container. It is stored in.

  The developing device D includes a developing roller 3 as a developer carrier that is rotatably provided, a supply roller 5, a regulating blade 4 as a regulating member that regulates toner on the developing roller and forms a toner coat layer on the developing roller. , Toner, and a developing container for storing them.

In the present embodiment, a φ12 mm elastic roller in which a conductive elastic layer 3 mm is formed on a core metal having an outer diameter φ6 mm is used as the developing roller 3. The supply roller 5 is an elastic sponge roller having an outer diameter of φ16 mm in which an elastic layer of insulating urethane sponge rubber having a volume resistance value of 10 ¹⁴ Ωcm is formed on a core bar having an outer diameter of φ6 mm.

  The developing roller 3 rotates in the forward direction (c direction shown in the drawing) with respect to the rotation direction of the photosensitive drum 1 while being in contact with the photosensitive drum 1, and the supply roller 5 is in contact with the developing roller 3. However, the developing roller 3 rotates in the opposite direction (direction d shown in the figure).

  The supply roller 5 adheres the non-magnetic one-component toner T in the developing container, conveys the toner to the contact surface with the developing roller 3, supplies the toner, and remains on the developing roller 3 without being developed at the developing unit. Is removed from the developing roller 3 and collected in the developing container.

  When the toner supplied from the supply roller 5 onto the developing roller 3 passes through the contact surface between the developing roller 3 and the regulating blade 4, the toner is charged by frictional charging and regulated by the coating layer thickness, and is charged to a predetermined level. A toner coat layer having an amount and a coat layer thickness is formed.

  A DC bias = −300 V is applied to the developing roller 3 during the image forming process, and the negatively charged toner in the above process causes a bright portion potential portion to be developed due to the potential difference in the developing portion contacting the photosensitive drum 1. The electrostatic latent image on the photosensitive drum is developed by flying only on the surface.

  The image forming apparatus A is based on a laser printer LBP5300 (manufactured by Canon Inc.), and items not specified in the embodiment are used without changing the settings in the specifications of the LBP5300.

<Examples and Comparative Examples>
Hereinafter, the configuration of the developing roller 3 and the development using the blade bias, which is a potential difference provided between the developing roller 3 and the regulating blade 4, by applying a bias to the regulating blade 4, which is a feature of the present embodiment. The apparatus will be described. In the following description, an example and a comparative example will be described.

<Example 1>
FIG. 1 is a cross-sectional view showing a schematic configuration of a developing device D having a developing roller 3 and a regulating blade 4, which is a developing device D applied to the image forming apparatus A and is a characteristic configuration of the first embodiment. It is.

  In this embodiment, the developing roller 3 can be supplied with a bias from a developing bias power source through the core of the developing roller 3. Further, the regulation blade 4 can be supplied with a bias from a blade bias power source through the conductive contact of the regulation blade 4. Here, the developing bias power source and the blade bias power source are provided in the developing device D or the image forming apparatus main body. The developing bias power source and the blade bias power source correspond to a potential difference setting unit.

Elastic layer of the developing roller 3 has a two-layer structure, a base layer 3 b covering the cored bar 3 c, provided on an outer peripheral side of the base layer 3 b, covers the base layer 3 b, the photosensitive drum 1 And the surface layer 3 a that is in direct contact with the regulating blade 4.

  In the examples and comparative examples described below, the thickness of the surface layer of the developing roller was measured using a thin film measuring apparatus “F20-EXR” (manufactured by Filmetrics Co., Ltd.).

The resistance of the base layer 3 b was set to a volume resistance value of 10 ⁶ Ω · cm so that the same potential as the bias applied to the core metal 3 c of the developing roller 3 was obtained on the surface of the developing roller 3.

Also, the base layer 3 b is to flex- stably abut against the photosensitive drum 1, with a silicone rubber such as JIS-A hardness of the developing roller 3 is 45 °.

On the other hand, the characteristic configuration in which the surface layer 3 a of the present embodiment, using an insulating urethane resin thin film.

Urethane resin layer as a surface layer 3 a is a polyurethane resin, and mainly of methyl ethyl ketone and diluted with an organic solvent mixed solution used as a main solvent, adding an isocyanate as a curing agent, sufficient that stirring the resin material liquid did. In this resin raw material liquid, a roller coated with an elastic base layer was dipped and dipped.

  The urethane resin thin film can have an arbitrary thickness without changing the physical properties of the urethane resin by changing the pulling speed during dipping coating. In this example, an insulating urethane resin thin film having a layer thickness of 0.9 μm as Example 1-A, a layer thickness of 1.7 μm as Example 1-B, and a layer thickness of 3.8 μm as Example 1-C is used as the surface layer. The developing roller was used.

Regulating blade 4, the supporting plate 4 a, and using what SUS (stainless steel) plate 4 b thick 80μm as the contact member is bonded, 2gf ^/ mm 2 (19 for the developing roller 3 The position is adjusted so as to contact with a pressure of 6 mN / mm ² ).

At the time of image formation, a DC bias of −600 V is applied to the regulating blade 4 through a support sheet metal 4 a by a blade bias power source, and a potential difference of −300 V is provided as a blade bias value for the developing roller 3. Will be.

<Example 2>
The schematic configuration of the developing device in the second embodiment is the same as that of the first embodiment, but in this embodiment, the configuration of the developing roller 3 is different from the first embodiment. The contact pressure of the regulating blade against the developing roller, the blade bias, and the like are set under the same conditions as in the first embodiment.

  The base layer of the elastic layer of the developing roller in this example is the same as in Example 1, but an insulating thin film mainly composed of silicon oxide containing carbon atoms (SiOx) is used as the surface layer. .

  The surface layer was formed using a plasma CVD (Chemical Vapor Deposition) method. Film formation by the plasma CVD method was performed by the following method.

  A roller coated with an elastic base layer made of silicone rubber is placed in a vacuum chamber, and a plate electrode is placed in close proximity to the roller. Thereafter, the chamber is filled with a gasified organosilicic compound serving as a source gas for the SiOx film and, if necessary, an inert gas, an oxidizing gas, or the like. Therefore, by rotating the roller and supplying high-frequency power between the roller and the plate electrode to generate plasma, molecules of the source gas grow on the surface of the elastic base layer to form a surface layer film. .

  The SiOx film can be changed depending on the composition of the source gas, the pressure concentration in the chamber of the source gas, the plasma irradiation time, and the like.

  In this example, as Examples 2-A to 2-F, development rollers having SiOx films having different thicknesses as surface layers were used. The SiOx film has a layer thickness of 0.3 μm as Example 2-A, a layer thickness of 0.5 μm as Example 2-B, a layer thickness of 0.9 μm as Example 2-C, and a layer thickness of 1. 4 μm, Example 2-E having a layer thickness of 2.5 μm, and Example 2-F having a layer thickness of 3.1 μm were used.

Since these SiOx films have different composition ratios of SiO and SiC, respectively, differences in physical properties are measured, but it has been confirmed that both exhibit insulating characteristics (this point will be described later). ). Further, the above-mentioned characteristics are that the composition ratio of oxygen and silicon (O / Si) and the composition ratio of carbon and silicon (C / Si) in the surface layer are as follows:
1.00 ≦ (O / Si) ≦ 1.95
0.05 ≦ (C / Si) ≦ 1.00
It was confirmed in the case of satisfying.

  The composition ratio was measured using an X-ray photoelectron spectrometer “Quantum 2000” (manufactured by ULVAC-PHI Co., Ltd.). Then, by using AlKα as the X-ray source, the binding energy of the Si 2p orbit and O and C 1s orbits on the surface of the developing roller are measured, and the abundance ratio of each atom is calculated from each peak value (O / The composition ratio of Si) and (C / Si) was determined.

<Comparative example>
The schematic configuration of the developing device in this comparative example is the same as that of the first embodiment, but the configuration of the developing roller 3 is different from that of the first embodiment in this comparative example. The contact pressure of the regulating blade against the developing roller, the blade bias, and the like are set under the same conditions as in the first embodiment.

  The base layer of the elastic layer of the developing roller in this comparative example is the same as in Example 1, but the surface layer is a conductive urethane resin film having a thickness of 10 μm.

The urethane resin is obtained by dispersing carbon black in the resin raw material liquid in the process of producing the urethane resin shown in Example 1, and the volume resistance value is 10 ⁶ Ω · cm due to the conductivity of the carbon black. I try to be about.

<Evaluation and discussion in each example and comparative example>
The relationship between the layer thickness of the high resistance surface layer and the blade bias, which is a feature of the present embodiment, will be described below.

<Definition of surface layer electrical properties>
The definition of the insulating film showing the characteristics of this embodiment will be described.

  In general, the bulk resistance of a solid is obtained from Ohm's law, but it is difficult to measure the resistance value of a thin film. In the case of a substance that solidifies the raw material solution as in Example 1, if a relatively thick film is formed on a sample stage such as a glass substrate, it can be measured by a four-terminal method or the like.

  However, the properties of the substance are generally different between the bulk and the interface, and when the film is thinned, the physical properties may be different because the influence of the physical properties of the interface on the bulk becomes large.

  In particular, in the method using chemical vapor deposition such as the CVD method shown in Example 2, since the film grows from the base layer interface, the base layer material tends to have a great influence on the physical properties of the surface layer film.

  Furthermore, even in a very thin film, even if the potential difference is such that dielectric breakdown does not occur, the leak current is generated, so that Ohm's law is not established, and the resistance value of the substance depends on the state of the film and the applied bias. It is different and difficult to define uniquely.

  In general, the electrical property of a substance follows Ohm's law, and since the value of a current flowing with respect to an applied bias is proportional, it can be defined as this proportional constant resistance value. However, a high resistance thin film material does not follow Ohm's law, and the resistance value decreases as the applied bias increases, and a phenomenon that current flows more easily is observed. This is presumably because the leakage current peculiar to the thin film increases according to the potential difference. As an example of this phenomenon, FIG. 4 shows the results of measuring the current value with respect to the applied bias for each of the developing rollers of Example 1-A, Examples 2-C, 2-D, and Comparative Example.

  Here, the measurement is performed by applying a predetermined bias to the developing roller rotating at 100 rpm while rotating the developing roller with a φ16 mm metal roller in contact with the developing roller. The current flowing after 60 seconds is measured. The contact area at this time was 190 mm in the longitudinal direction (axial direction) width of the roller and 1 mm in the rotational direction width.

  As can be seen from this result, in any of the developing rollers, a current easily flows rapidly with a specific applied bias having a threshold value. Therefore, from this measurement method, it is not possible to find a large difference in characteristics between the developing roller shown in the example, which seems to have a high resistance of the surface layer, and the developing roller having a relatively low resistance of the surface layer. difficult.

  On the other hand, using the same measuring means, the change in the current value with the passage of time immediately after the bias was applied was also measured.

The result is shown in FIG. Note that the bias applied to each developing roller at this time is measured in a stable state, that is, in a condition that at least becomes a value larger than the threshold value shown in FIG. Specifically, the measurement was performed under the condition that the current density of the current 60 seconds after the bias application was 0.5 μA / mm ² or more. This current density is a value obtained by dividing the value of the current flowing between the metal roller and the developing roller by the contact area between the metal roller and the developing roller.

  From the results of FIG. 5, the current values of the developing rollers shown in Examples 1 and 2 show a tendency to greatly decrease with the lapse of time immediately after the bias application, whereas the development of the comparative example It can be seen that the roller does not show a large change in the current value. This phenomenon can be understood by considering the relationship between the surface layer sandwiched between the base layer of the developing roller, which is a conductor, and the metal roller facing it as an electric circuit.

  In the case of the comparative example, the surface layer can be simply considered as a resistor. However, in the case of the developing rollers of Examples 1 and 2, the resistance value of the surface layer is very large. Considered as a parallel circuit. Therefore, it is considered that this circuit has a time constant, and a phenomenon in which the current value decreases with the passage of time appears.

  That is, in the measurement, if a phenomenon in which the current value decreases with the passage of time is observed, it can be said that the surface layer has a very high resistance value.

As a value indicating the change of the current value with respect to the time change, each developing roller is set with respect to Log (It / Is) which is a logarithm of the ratio between the current value It after 2 seconds of bias application and the current value Is after 60 seconds. The results obtained using these are shown in FIGS. Here, Log represents a common logarithm.

  When there is no change in current value with respect to time, the value in logarithmic display is zero.

  In the developing rollers of Example 1 and Example 2 that are considered to have very high resistance values, all of the values are positive, indicating at least 0.1 or more. On the other hand, the developing roller of the comparative example shows a value less than or equal to 0 because there is no change in the current value over time, and the difference from the developing roller of the embodiment can be seen.

  At least, in the case of a developing roller having a thin surface layer with respect to the base layer, when a decrease in current value is observed with a time constant when bias is applied, the resistance value of the surface layer with respect to the base layer resistance Can be defined as very high.

  The developing roller having a surface layer having a very high resistance value defined here can be expected to have a high pressure resistance against bias application.

  In FIG. 7, the horizontal axis is arranged in the order of the thickness of the surface layer, but when viewed as the relationship between the layer thickness and the value of Log (It / Is), the value of Log (It / Is) is the layer thickness. It increases with time, but it seems to decrease on the contrary.

  This phenomenon occurs when the layer thickness is small, the leakage current decreases as the layer thickness increases, so that the capacitance of the surface layer capacitor increases, but the thickness of the layer thickness where the leakage current is sufficiently small Then, it can be understood that the capacity decreases as the layer thickness increases.

  In addition, the phenomenon in which the value of Log (It / Is) in the comparative example shows a slight minus is a phenomenon generally observed in a conductor having a relatively high resistance. The current flows between the conductive materials such as conductive particles dispersed in the conductor, and the current flows between them. However, the current flows, and the current flows easily between the sites due to the orientation. Conceivable.

<Blade bias effect>
Using each of the developing rollers of Example 1, Example 2, and Comparative Example, the blade bias was changed, and image evaluation in each case was performed.

  FIGS. 8 and 9 show the measurement results of the change in image density in cyan toner when the blade bias is changed using the developing rollers in Example 1-B and Example 2-C, respectively. The image density was measured using a 504 spectral densitometer manufactured by X-Rite Co., Ltd.

  It was found that the image density with respect to the blade bias changes with different threshold values for each developing roller. 8 and 9, it can be seen that the density increases as the blade bias value increases and is stable at a certain value.

  When viewed on the image in the range of the bias value where the increase in density is recognized due to the blade bias, nonuniform unevenness is recognized in the image. On the other hand, at a certain bias value or higher, there was no increase in density, and an image with a stable density had no such unevenness, and a uniform image was obtained.

  That is, it can be said that the increase in the image density is due to the fact that a part with a high density occurs on the image and this region becomes wider as the bias value is increased. For this reason, here, where the image unevenness is eliminated and a uniform image is obtained, the threshold value of the image density increase phenomenon due to the blade bias value (a value at which the blade bias effect can be obtained) is used.

  When the change in image density with respect to the blade bias value was measured for the developing rollers of Example 1, Example 2, and Comparative Example, the same threshold was recognized in all the developing rollers. FIG. 10 shows the relationship between the layer thickness of the surface layer of each developing roller and the threshold value.

As can be seen from FIG. 10, except for the comparative example having a surface layer of 10 μm, the threshold values of all the developing rollers are substantially in a straight line, and the straight line indicates that the blade vise is Vb (V), and the layer of the surface layer If the thickness is t (μm),
Vb = 55 × t
It was possible to approximate.

  The presence of the saturation value of the image density is considered to be related to the fact that there are threshold values for the blade bias and the current value of the surface layer. As described above, for the developing roller other than the comparative example, the surface layer has a very high resistance value under the blade bias condition that does not exceed the threshold value. Therefore, the potential of the developing roller surface at the contact portion with the regulating blade is Close to the surface potential with the regulating blade. Therefore, there is no electric field formation between them, and no influence on the toner occurs.

  On the other hand, when a blade bias exceeding the threshold is applied, the resistance value of the surface layer decreases to some extent, and accordingly, the potential on the surface of the developing roller approaches the bias value applied to the original developing roller. As a result, a potential difference is generated between the regulating blade and the surface of the developing roller, and the toner passing through this is affected by this electric field, and the toner conveyance amount, charge application, and the like change. 8 and 9, the threshold value in blade bias is higher in Example 1-B, in which the surface layer is thicker, and the density change amount is increased accordingly. This indicates this phenomenon.

  According to the above mechanism, the threshold value is considered to be affected by the resistance value as a material as well as the thickness of the surface layer.

  In this regard, paying attention to the developing rollers of Example 1-A, Example 2-C, and Example 2-D shown in FIG. 4, the surface layer thickness of each developing roller is that of Example 1. -A and Example 2-C are almost the same, whereas Example 2-D is about 1.5 times.

  On the other hand, the behavior of the current value with respect to the applied voltage shown in FIG. 4 is very similar between Example 1-A and Example 2-D having different thicknesses, but the thickness is almost the same. There is a significant difference between Example 1-A and Example 2-C. From this, it can be said that the surface layer of Example 1-A has a significant difference in resistance value as a material with respect to the surface layer of Example 2-C and Example 2-D.

  However, it can be said that such a difference in resistance value is very small in the effect of the blade bias in these developing rollers as compared with the influence on the thickness of the surface layer as shown in FIG.

  The reason for this is considered to be that when the resistance value of the surface layer is very high, the phenomenon that the resistance value changes due to the applied bias is largely related to the thickness of the surface layer, mainly due to leakage current. That is, if the resistance value as a material is a surface layer within a certain range, it can be said that the threshold value of the blade bias concentration change can be expressed in relation to the surface layer thickness.

  In the measurement shown in FIG. 4, there is no toner layer that becomes a high resistance layer between the surface of the developing roller and the regulating blade, which exists during actual image formation. For this reason, the threshold value of the voltage at which the current value changes greatly at this time is not necessarily the same as the threshold value of the density change due to the actual blade bias.

<Upper limit of blade bias>
With respect to the upper limit value of the blade bias, the occurrence of abnormal images was evaluated.

When a high blade bias was applied, three phenomena were mainly observed as abnormal images. The three phenomena are shown as abnormal images (A) to (C) below.
(A) Horizontal streak: An image streak on a straight line that occurs randomly, and the number increases as the bias is increased.
(B) White spots: A large number of very small white spots at the initial stage of occurrence. When the bias value is increased, the generation range is widened and the size of the white spots is increased.
(C) Fog: The original white background is developed by increasing the bias.

  The above phenomenon may occur in all developing rollers. However, if any phenomenon occurs, it becomes difficult to apply a higher blade bias. Could not be confirmed.

  When the blade bias is raised using the developing rollers of Example 1, Example 2, and Comparative Example, the abnormal images (A) to (C) that are generated first and the blade bias value at that time are shown. As shown in FIG.

  For the abnormal image (A), it is considered that a surge current flows in the surface layer and the potential on the surface of the developing roller becomes the same potential as that of the regulating blade. Therefore, it is considered that the first problem appears with a thin film having a relatively low pressure resistance.

  The abnormal image (B) is considered to be related to the discharge phenomenon from the generated potential difference and the appearance of the generated image. The abnormal image (B) is generated with a bias that is about several tens of volts lower than the potential difference at which the discharge phenomenon occurs in the air gap. Thus, the presence of the toner layer lowers the potential of the discharge limit, and a discharge phenomenon occurs. At that time, a large amount of charge moves using the toner as a medium. It appears to occur on the image as a white spot.

  The abnormal image (C) is considered to be caused by the fact that the surface potential of the developing roller increases due to the blade bias, and the difference from the potential of the white background portion of the photosensitive drum disappears. This occurs when the volume resistance is higher than the surface resistance of the surface layer, and is likely to occur when the surface layer is thick.

  The results shown in FIG. 11 are shown in FIG. 12 as the relationship between the abnormal image occurrence limit bias value and the surface layer thickness.

  From FIG. 12, it can be seen that the occurrence limit bias value of the abnormal image increases linearly with the increase of the layer thickness up to the vicinity of the layer thickness of 2 μm, but is almost constant thereafter.

  Here, when the surface layer is 2 μm or less, the abnormal image is (A) or (B), whereas when the surface layer is 2 μm or more, the abnormal image is (C). .

  The occurrence of the abnormal image (A) or (B) is related to the pressure resistance performance of the surface layer, and the generation limit value is expected to increase as the layer thickness increases. In contrast, the abnormal image (C) is a phenomenon that is likely to occur due to an increase in the resistance value of the surface layer, and is expected to be likely to occur due to an increase in the layer thickness.

  The difference Vb−d (V) (= Vb−Vd) of the surface potential Vd (V) on the developing roller with respect to the applied blade bias Vb (V) when the measurement of FIG. 5 was performed was measured. FIG. 13 shows the relationship between the layer thickness and Vb-d in the case of Vb = 200V and Vb = 300V. From this result, it can be seen that the surface potential drop of the developing roller suddenly increases with the developing roller having a surface layer thickness exceeding 2 μm.

  As a result, when the thickness of the surface layer exceeds 2 μm, the surface potential of the developing roller is difficult to maintain the same potential with respect to the bias applied to the core of the developing roller, and an abnormal image ( It can be seen that a phenomenon such as C) is likely to occur.

From FIG. 12, the abnormal image occurrence limit value can be approximated as follows. That is, the abnormal image generation limit value is as follows when the surface layer thickness is 2 μm or less.
Vb <120 × t + 250
It can be approximated as follows. In the case where the thickness of the surface layer is 2 μm or more,
Vb <500
It can be approximated as follows.

  As expected, the developing roller of the comparative example generates an abnormal image with a lower blade bias than the developing roller of the example. The fact that this blade bias shows a value close to 250V, which is the intercept of the above equation, is considered to indicate that the pressure resistance performance of the high resistance surface layer in the example functions from a considerably thin region. .

<Effective blade bias area>
As a summary of the results, FIG. 14 shows an effective region of the blade bias Vb (potential difference Vb) with respect to the layer thickness of the surface layer.

In a developing roller having a surface layer, when the surface layer is a high resistance layer having a capacitive component, the current value after 2 seconds from the bias application is It and the current value after 60 seconds is Is. Here, in a developing roller having a surface layer, the case where the surface layer is a high resistance layer having a capacitive component, that is, a current flowing between a metal roller in contact with the developing roller and the developing roller. Is applied under a bias application condition such that the current density becomes 0.5 μA / mm ² or more. At this time,
Log (It / Is)> 0.1
Where at least the layer thickness t (μm) of the surface layer is
0 <t <4.00
In this range, the blade bias Vb (V) is
Vb> 55 × t
The blade bias effect is obtained when the above relationship is satisfied.

Also,
In the range of 0 <t ≦ 2.00, Vb <120 × t + 250,
In the range of 2.00 <t <4.00, Vb <500
By doing so, it is possible to suppress the occurrence of image defects due to blade bias.

  In the developing roller having the conductive surface layer shown in the comparative example, the blade bias effect was obtained at 60V or higher, whereas the image defect occurred at 280V. The effective range is 220V, which is clearly narrower than the present embodiment. Even when the surface layer thickness of the comparative example is reduced from 10 μm, the effective lower limit value of the blade bias does not widen by 60 V or more, and the abnormal image at the effective upper limit value of the blade bias is (C). Even when the thickness is increased, the upper limit cannot be expected to increase.

  Therefore, in the developing roller having a high resistance and a thin surface layer described in the present embodiment, the blade bias can be used in a wider range than the developing roller having the conductive surface layer shown in the comparative example. It became possible.

<Advantage of SiOx film by CVD method>
By using dry vapor deposition represented by the CVD method, even an ultra-thin film of 1 μm or less can be stably formed.

  In this embodiment, the surface layer of the developing roller is characterized by using a high-resistance material in a thin layer as compared with the conventional surface layer shown in the comparative example. As described above, since the thickness unevenness of the surface layer appears in a large difference in physical properties, a stable and uniform film forming method is important.

  In film formation with a wet paint, the viscosity of the solution and the problem of dispersibility due to the dispersion material in the solution tend to be problems with respect to the uniformity of thickness. Also, when there is uneven shape on the surface of the base layer, a film is formed so as to fill the shape due to the surface tension of the solution, so it tends to cause uneven thickness, and the thinner the surface layer, the more uniform it can be made. was difficult.

  On the other hand, in the vapor phase growth method, the source material adheres on the surface of the base layer in atomic or molecular units, and is further grown to form a film. For this reason, a uniform ultra-thin film from the nano order is possible, and even when there is a shape unevenness on the surface, it is possible to form a surface layer with a uniform film thickness along the shape unevenness.

In the developing roller using the SiOx film as the surface layer shown in Example 2, even when the surface layer has a minimum thickness of 50 nm, the increase in density can be confirmed when the blade bias value is about several volts, It was confirmed that at least about 300 V, no abnormal image was generated. Therefore, as the layer thickness t (μm) of the surface layer,
0.05 <t <4.00
Is more preferable.

  The SiOx film is characterized by the flexibility of the film in its composition ratio. A thin film having only a composition of Si—O or Si—C is very hard, but a thin film having both compositions has flexibility.

  Here, when an elastic body is used for the base layer of the developing roller, if a hard thin film is used as the surface layer, the surface layer cannot follow the deformation of the base layer, and there is a concern that the surface layer may be damaged such as cracks. Is done.

  On the other hand, the developing roller having the surface layer shown in Example 2 has a composition of Si—O and Si—C, and the surface layer having a thickness of 4 μm or less is at least in the example. Even on the very flexible base layer used, surface damage such as cracks did not occur.

As described above, in this embodiment,
Log (It / Is)> 0.1
A developing roller having a high resistance component and a capacitance component satisfying the above requirements is used. As a result, the pressure resistance performance of the developing roller can be improved against the potential difference provided between the developing roller and the regulating blade by the potential difference setting means. For the potential difference (blade bias) Vb (V), the thickness t (μm) of the surface layer of the developing roller is
In the range of 0.05 <t <4.00, Vb> 55 × t
It is said. As a result, the coating amount of the developer layer can be increased, and effects such as an increase in image density can be obtained. As described above, according to the present embodiment, the effective potential difference width (effective area of the applied bias) provided between the developing roller and the regulating blade is widened as compared with the developing roller having the conventional surface layer. Is possible.

Here, while the developing roller is driven to rotate with the metal roller, the bias current is applied so that the current density of the current flowing between them is 0.5 μA / mm ² or more in a stable state. The current value after 2 seconds from the bias application is It, and the current value after 60 seconds is Is.

Further, regarding the potential difference Vb (V) and the thickness t (μm) of the surface layer of the developing roller,
In the range of 0.05 <t ≦ 2.00, Vb <120 × t + 250
age,
In the range of 2.00 <t <4.00, Vb <500
It was. This makes it possible to suppress the occurrence of abnormal images at the time of a high potential difference.
Here, in this embodiment, the film thickness t of the surface layer is defined within a range of 4 μm or less. This is because the effect of the present invention could be verified within a range of 4 μm or less. Although it may be possible to obtain the effects of the present invention even at a film thickness of 4 μm or more, the film thickness is increased.
In the present invention, the effect was verified by limiting the film thickness to 4 μm or less.

  In addition, by forming the surface layer of the developing roller by vapor phase growth, it is possible to form a surface layer that is thin but excellent in uniformity, which is an important condition when a high resistance material is used as the surface layer.

Further, the surface layer of the developing roller is formed of silicon oxide containing carbon atoms, and the oxygen and silicon composition ratio (O / Si) in the surface layer is determined.
1.00 ≦ (O / Si) ≦ 1.95,
Carbon and silicon (C / Si)
0.05 ≦ (C / Si) ≦ 1.00
It was. As a result, it is possible to provide a flexible surface layer that is free from cracks and the like even when the elastic base layer is deformed.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of the developing device according to the first exemplary embodiment. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment. FIG. 4 is a cross-sectional view illustrating a schematic configuration of one of four process cartridges arranged in parallel in the image forming apparatus according to the embodiment. FIG. 6 is a diagram showing a change in current amount with respect to a bias value when a bias is applied to the developing roller. FIG. 6 is a diagram illustrating a change in current amount with respect to time when a bias is applied to the developing roller. The figure which shows the ratio of the electric current value after 2 second and 60 second after a bias application to a developing roller. The figure which shows the ratio of the electric current value after 2 second and 60 second after a bias application to a developing roller. The figure which shows the image density change in blade bias application. The figure which shows the image density change in blade bias application. The figure which shows the relationship between the layer thickness of the surface layer of a developing roller, and a threshold value (value from which a blade bias effect is acquired). The figure which shows the abnormal image generation result by blade bias application in a developing roller. The figure which shows the relationship between the generation limit bias value of an abnormal image, and the layer thickness of a surface layer. The figure which shows the surface potential fall amount of the developing roller with respect to the layer thickness of a surface layer. The figure which shows the effective area | region of a blade bias with respect to the layer thickness of a surface layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Developing roller 3 a Surface layer 3 b Base layer 4 Regulating blade 4 a Support sheet metal 4 b SUS plate D Developing device

Claims (2)

A developer carrier provided rotatably with a base layer having conductivity and elasticity, and a surface layer provided on an outer peripheral side of the base layer;
A regulating member that has conductivity and is provided so as to contact the developer carrier, and that regulates one-component developer on the developer carrier;
A potential difference setting means for generating a potential difference between the developer carrier and the regulating member;
In a developing device comprising:
The developer carrying member is formed between the developer carrying member and the metal roller while rotating the developer carrying member with the metal roller being in contact with the developer carrying member so as to be driven to rotate. When bias application is performed so that the current density of the current flowing between them is 0.5 μA / mm ² or more in a stable state,
Assuming that current values after 2 seconds and 60 seconds after the bias application are respectively It and Is, and Log indicates a common logarithm,
Log (It / Is)> 0.1
Satisfying,
When the potential difference is Vb (V) and the thickness of the surface layer of the developer carrier is t (μm),
0.05 <t <4.00,
In the case of 0.05 <t ≦ 2.00, 55 × t <Vb <120 × t + 250
In the case of 2.00 <t <4.00, 55 × t <Vb <500
Meet the,
The surface layer of the developer carrier is formed of silicon oxide containing carbon atoms,
The composition ratio of oxygen and silicon (O / Si) and the composition ratio of carbon and silicon (C / Si) in the surface layer are as follows:
1.00 ≦ (O / Si) ≦ 1.95
0.05 ≦ (C / Si) ≦ 1.00
A developing device according to claim Succoth meet.   The developing device according to claim 1, wherein the surface layer of the developer carrying member is formed by vapor phase growth.

Images