Patent Application
20130223891
The present invention relates to a development device used in an image forming apparatus that employs an electrophotographic method.
Existing image-forming apparatuses are known to experience a phenomenon called ghosting in which the history of image formation appears as afterimages in subsequent image formation. For example, when a halftone image is formed after formation of a high-density solid image, the trace of the solid image often appears in the halftone image, resulting in ghosting. Also known is a phenomenon in which the density at a back end of an image is low when a high-density solid image is formed.
In order to suppress ghosting and the decrease in density at the back end of a solid image, a supply roller (toner supplying member) that contacts a developing roller (toner bearing member) and supplies and removes the toner is widely employed in typical development devices. That is, ghosting can be suppressed by erasing the history of the image formation remaining on the developing roller by using the removing action of the supply roller. The decrease in density at the back end of a solid image can be suppressed by supplying new toner from the supply roller to the developing roller.
However, a development device not quipped with the supply roller has been proposed to reduce the size and cost of the development device.
PTL 1 and PTL 2 each propose a development device that includes a toner bearing member employing a structure in which dielectric portions are scattered on its surface but that does not include a supply roller. That is, the dielectric portions on the surface of the toner bearing member are rubbed with a toner layer thickness regulating member (regulating member) either directly or with the toner therebetween so as to charge the dielectric portions and form microfields between the dielectric portions and surrounding regions thereof. The toner transported to the surface of the toner bearing member receives gradient force from the microfields and becomes attracted to the surface of the toner bearing member, and thus the toner bearing member bears the toner. In PTL 1 and PTL 2, it is described that in order to stabilize the charge amount of the toner on the toner bearing member, the position of the dielectric portions in a triboelectric series should be on the polarity side, relative to the regulating member, opposite to the normal charge polarity (charge polarity for developing electrostatic latent images) of the toner. For example, when the toner is negatively charged, the triboelectric series should be (−) toner<regulating member<dielectric portions (+).
PTL 1 Japanese Patent No. 03272056
PTL 2 Japanese Patent No. 03162219
However, studies conducted by the inventors have found that when the position of the dielectric portions in the triboelectric series is on the polarity side, relative to the regulating member, opposite to the normal charge polarity of the toner as in the related art, ghosting is likely to occur. According to the structure of the related art, the toner electrostatically strongly adheres to the dielectric portions, resulting in difficulty to regulate the thickness of the toner layer and there is a tendency of not being able to sufficiently erase the history of previous image formation remaining on the developing roller.
Accordingly, an object of the present invention is to suppress the decrease in density at the back end of a solid image and occurrence of ghosting in a development device that does not have a toner supply member that contacts a toner bearing member and supplies and removes the toner.
To achieve the object described above, a first invention according this application is a development device that includes a container that contains a toner, a toner bearing member that has dielectric portions scattered on a surface thereof and bears the toner, and a regulating member that regulates a layer thickness of the toner on the toner bearing member, in which a position of the dielectric portions in a triboelectric series is on the same polarity side, relative to the regulating member, as a normal charge polarity of the toner.
To achieve the object described above, a second invention according to this application is an image forming apparatus that includes a development device that includes a container that contains a toner, a toner bearing member that has dielectric portions scattered on a surface thereof and bears the toner, and a regulating member that regulates a layer thickness of the toner on the toner bearing member; and a voltage applying device that applies a voltage to the regulating member so that a potential difference obtained by subtracting a potential of the dielectric portions from a potential of the regulating member has a polarity opposite to a normal charge polarity of the toner.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An image forming apparatus according to the present invention will now be described in further detail by referring to drawings. The embodiments described below are merely illustrative and the dimensions, materials, shapes, relative positions, etc., of the structural components described below do not limit the scope of the present invention unless specifically described.
The exposure device 91 and a reflecting mirror 92 are arranged so that a laser beam emitted from the exposure device 91 reaches an exposure position A on the photosensitive drum 1 via the reflecting mirror 92. The transfer roller 93 is disposed under the photosensitive drum 1. A transfer material S after the transfer is conveyed to the fixing unit 94. The cleaning device 8 is disposed downstream of the transfer position in the drum moving direction. An attached blade is arranged to make contact so as to scrape off the toner on the photosensitive drum 1.
The image forming operation of the image forming apparatus will now be described. A controller 70 generally controls the following image forming operation in accordance with a particular control program and lookup tables. First, the surface of the photosensitive drum 1 rotating in the arrow R1 direction at 100 mm/sec is charged to a particular potential by using the charging roller 7. At the exposure position A, an electrostatic latent image is formed on the photosensitive drum 1 with a laser beam emitted from the exposure device 91 in accordance with an image signal. The formed electrostatic latent image is developed at a development position C with the development device 2 to form a toner image. The toner image formed on the photosensitive drum 1 is transferred to the transfer material S at a transfer position B. The transfer material S serving as a recording medium and onto which the toner image has been transferred is conveyed to the fixing unit 94. The fixing unit 94 pressurizes and heats the toner image on the transfer material S to fix the toner image on the transfer material S and form a final image.
Next, the structure of the development device according to this embodiment is described.
The development device 2 of this embodiment includes a development container 6, a development roller 3, and a regulating blade 4 as shown in
The present invention involves a structure in which a toner supply member in contact with the development roller 3 is omitted and the aforementioned gradient force is used to bear two or more layers of toner on the surface of the development roller 3. Accordingly, dielectric portions and conductive portions are provided on the surface of the development roller 3 and the surface is rubbed with the regulating blade 4 through the toner so as to charge the dielectric portions and form microfields on the portions adjacent to the conductive portions. The toner transported to the surface of the development roller 3 receives the gradient force from the microfields and becomes borne on the surface of the developer bearing member by being attracted thereto.
The surface of the development roller 3 of this embodiment is configured so that dielectric portions that can retain charges and conductive portions adjacent to the dielectric portions both having small areas are mixed and exposed. In particular, as shown in
The size of the dielectric portions 31 is preferably about 5 to 500 μm in outer diameter. This is a value optimum for retaining charges on the surface and suppressing banding. When the outer diameter is larger than 5 μm, sufficient charges can be retained on the surface of the dielectric portions 31 and sufficient microfields can be formed. When the outer diameter is less than 500 μm, the difference in potential between the dielectric portions 31 and conductive portions 32 is not excessively large and the banding can be suppressed. Furthermore, the dielectric portions 31 are required to retain an appropriate degree of potential difference with respect to the conductive portions 32 and retain microfields during the period from when the dielectric portion passes the toner layer thickness regulating position defined by the regulating blade 4 to when the dielectric portion passes the toner layer thickness regulating position next time (the rotation period T of the development roller 3). Accordingly, the electrical resistance R and the capacitance C of the dielectric portions 31 preferably satisfy CR≧T/Ln10 (Ln: natural logarithm) with respect to the rotation period T of the development roller 3. In this manner, the dielectric portions 31 charged at the toner layer thickness regulating position by the regulating blade 4 can retain at least 10% of the charge amount after elapse of the rotation period T. In this embodiment, the above-described relationship is satisfied and the microfields are retained with CR≧0.091.
In order to form microfields indicated by electrical flux lines E shown in
The volume resistivity of dielectric particles was measured by applying a voltage of 1000 V to a measurement sample for 30 seconds using a resistivity meter Hiresta-UP produced by Mitsubishi Chemical in a 23° C./50% RH environment. The amount of the measurement sample used is preferably appropriately adjusted by considering the particle density or the like of the object to be measured. For example, when measuring acrylic resin particles, 0.6 g of the particles are compacted under a pressure of 2000 kgf/cm2 and used as the measurement sample. The dielectric constant of the dielectric particles is measured as follows. First, a powder sample is placed in a cylinder having a base area of 2.26 cm2 and 15 kg of pressure is applied to the upper and lower electrodes. Simultaneously, an AC voltage of 1 Vpp and 1 MHz is applied and the current at that time is measured. The results are normalized to calculate the dielectric constant. The CR measurement of the dielectric portions 31 on the surface of the development roller 3 may be replaced by charging the dielectric portions 31 by a particular method and measuring the attenuation rate thereof. For example, a measurement sample having a 1 cm×1 cm surface and a thickness of 3 mm is cut out from the development roller 3 and irradiated with plus ions from ZEROSTAT 3 produced by MILTY Products Limited. Then the potential of the dielectric portions 31 is measured with a scanning probe microscope (SPA300, produced by SII Nanotechnology Inc.) in a KFM mode at particular time intervals and CR can be calculated from the potential attenuation rate.
In order to form the surface layer 30c shown in
Although details are described below, the development system of this embodiment uses the relationship among the work functions of the dielectric portions 31 on the surface of the development roller 3, the charging layer 41 of the regulating blade 4, and the toner. The work function of the material used in the dielectric portions on the surface of the development roller 3 was 5.7 eV when measured with a surface analyzer (AC-2 produced by Riken Keiki Co., Ltd.) at an irradiation dose of 250 nW.
The regulating blade 4 in this embodiment has a charging layer 41a. In particular, it is prepared by laminating the polyamide resin on a phosphor bronze metal thin sheet. The thickness of the phosphor bronze metal thin sheet was 0.1 mm and the thickness of the polyamide resin was 0.1 mm in this embodiment. The work function of the charging layer 41 determined by the aforementioned measurement method was 5.42 eV.
A negatively chargeable toner that uses a non-magnetic styrene acryl-based+polyester-based resin was used as the toner 5 of this embodiment. The work function of the toner 5 measured by the aforementioned method was 6.01 eV.
In this embodiment, a DC voltage of −300 V was applied as the development bias for contact development to the development roller 3 from a DC power source 61 and a latent image was designed on the photosensitive drum 1 so that the potential of a solid white image portion was −500 V and the potential of a solid image portion was −100 V. In this embodiment, in order to obtain a preferable image density, the toner coat amount on the photosensitive drum 1 during formation of the solid image needs to be 0.54 mg/cm2 and in order to achieve this, the toner coat amount on the development roller 3 needs to be 0.45 mg/cm2.
In this embodiment, the materials for the dielectric portions 31 of the development roller 3, the charging layer 41 of the regulating blade 4, and the toner 5 are selected so that the above-described work functions are achieved and that the order in the triboelectric series is (−) toner 5<dielectric portions 31<charging layer 41 (+). According to this structure, friction between the toner 5 and the charging layer 41 and between the toner 5 and the dielectric portions 31 can impart negative charges to the toner 5 and positive charges to the charging layer 41 and the dielectric portions 31. Moreover, according to the triboelectric series described above, friction between the toner 5 and the charging layer 41 and between the toner 5 and the dielectric portions 31 generates a potential difference between the surface of the development roller 3 and the surface of the charging layer 41 so that the toner 5 migrates to the charging layer 41.
The development system of this embodiment is described below with reference to
First, formation of a solid image is described. As shown in
Next, formation of a solid white image is described. As with the formation of a solid black image, microfields described above are formed between the dielectric portions 31 and the conductive portions 32 at the regulating position. In the development portion, as shown in
The ghost image suppressing mechanism featured in the present invention will now be described in detail with reference to
The mechanism with which the toner adheres to the surface of the development roller 3 during formation of a solid image is described with reference to
Next, the mechanism with which the toner layer on the surface of the development roller 3 is regulated by the regulating blade 4 during formation of a solid image is described with reference to
In other words, in this embodiment, the toner coat amount after passing the regulating position is made the same between when a solid image is formed and when a solid white image is formed due to the toner adhering mechanism to the surface of the development roller 3 and the toner layer regulating mechanism discussed above so that occurrence of ghost images can be significantly suppressed. Here, a detail description is provided by comparing the formation of a solid image and formation of a solid white image in which the difference in the condition of the toner coating on the surface of the development roller 3 is most obvious. However, the toner coat amount after passing the regulating position can be made the same due to the aforementioned mechanisms even during formation of a halftone image. Images were formed on 1000 A4 size sheets by using the image forming apparatus of this embodiment shown in
As discussed above, the image forming apparatus of this embodiment includes the development roller 3 having dielectric portions 31 scattered on the surface and other components are configured so that, in a triboelectric series, the position of the dielectric portions 31 is on the same polarity side, relative to the regulating blade 4, as the normal charge polarity of the toner. In this manner, an image forming apparatus that includes a development device having no developer supply member, suppresses the decrease in density at the back end of a solid image, and suppresses occurrence of ghosting can be provided.
In this embodiment, the materials for the development roller 3, the regulating blade 4, and the toner 5 are as described above but are not particularly limited as long as the position of the dielectric portions in a triboelectric series is on the same polarity side, relative to the regulating blade 4, as the normal charge polarity of the toner. For example, when the toner is positively charged, the materials should be selected so that (−) charging layer 41<dielectric portions 31<toner 5 (+) and that the potential relationship among the conductive portions 32, the dielectric portions 31, and the charging layer 41 is as shown in
The effects of the present invention can be achieved regardless of whether the charging layer 41 is electrically conductive or insulating. In order to prevent charge up on the elastic blade and prevent the toner from carrying unnecessary charges, the charging layer 41 is preferably electrically conductive.
In order to further enhance the effects of the present invention, as shown in
The development roller 3 of this embodiment has a structure in which dielectric portions 31 are scattered on the surface. Here, “scatter” means not only a state in which dielectric portions are separated from one another but also a state in which dielectric portions are continuous as shown in
In this embodiment, the photosensitive drum 1 and the development roller 3 are configured to make direct contact with each other. Alternatively, in order to eliminate the pressure applied to the toner during contact development, the photosensitive drum 1 and a development roller 3a may be arranged in a non-contact manner as shown in
Next, another embodiment of the image forming apparatus according to the present invention is described.
The feature of this embodiment is that, in the image forming apparatus described in embodiment 1, the surface of the development roller 3 has protrusions and the dielectric portions 31 are present in the protrusions as shown in
In this embodiment, the development roller 3 includes an elastic layer 30b composed of a conductive rubber material and a surface layer 30c on the outer periphery of an axial core 30a as shown in
In formula (B), R1 represents a linear alkylene group having 2 or more and 9 or less carbon atoms or a branched alkylene group having 6 or more and 9 or less carbon atoms and R2 represents a linear alkylene group having 2 or more and 8 or less carbon atoms.
This surface layer features that the domain phase constituted by dielectric portions and the matrix phase constituted by conductive portions in which conductive fine particles are localized are mixed and exposed in small areas. The domain phase functions as dielectric portions 31b and the matrix phase functions as the conductive portions 32b described above. When the dielectric portions 31b are charged by a particular method, microfields are formed as indicated by electrical flux lines E shown in
The equivalent circle diameter of the dielectric portions 31b is preferably 10 μm or more. At 10 μm or more, a sufficient charge potential amount for retaining the toner can be obtained. The equivalent circle diameter here refers to a diameter of a circle having the same area as the area of the domain phase projected onto the development roller surface. The domain phase in the present invention can be identified with a scanning electron microscope (SEM), scanning transmission electron microscope (STEM), or the like. As for the area ratio of these portions, the area of the dielectric portions is controlled to account for about 50% of the entirety. In this embodiment, the thickness of the surface layer 30c is 10 μm. The surface roughness of the development roller 3 having protruding dielectric portions can be controlled by controlling the phase separation structure. An example of the method for forming a coating film having a sea-island type phase separation structure is a method with which a highly crystalline resin material solid at room temperature is dissolved in an solvent in a supersaturated amount so as to form a coating film. A highly crystalline resin material has a property to easily precipitate into crystals in some parts by evaporation of the solvent during formation of the coating film. These precipitated sites of the crystals that are protruded form the domain portions and the portion where the coating film is continuous forms a matrix portion so as to form a sea-island type phase separation structure. The domain phase, i.e., the degree of precipitation of crystals, depends on the crystallinity of the polyester copolymer resin in this embodiment. The important point is that the crystallinity of the polyester copolymer resin is controlled in terms of crystal size and coverage by optimizing the molecular structure. The phase separation structure, i.e., the size of the domain, can be controlled through the boiling point and evaporation speed of the solvent and SP value in addition to optimizing the crystallinity of the resin material.
The localization of the conductive fine particles in the matrix phase was confirmed through mapping analysis with a scanning probe microscope (SPM). As a result, it has been found that whereas the region in the domain shape exhibits insulating property, the surrounding matrix region exhibits electrical conductivity. The work function of the material used in the dielectric portions on the surface of the development roller 3 was 5.6 eV when measured with a surface analyzer (AC-2, produced by Riken Keiki Co., Ltd.) at an irradiation dose of 250 nW.
In this embodiment, as shown in
The ghost image suppressing mechanism of this embodiment will now be described. This embodiment differs from the embodiment 1 in that the dielectric portions 31 are present in the protrusions and the polarity may be negative or positive depending on the relationship between the height of the protrusions and the toner particle diameter. However, as discussed in the embodiment 1, attraction of the toner to the surface of the development roller 3 according to the present invention occurs due to the gradient force of the microfields. Thus, the direction of the force the toner receives is the direction in which the magnitude of the electric field increases regardless of the direction of the electric field. The case in which the dielectric portions 31 are negatively charged is described in detail in the embodiment 3. Thus, the mechanism with which ghost images are suppressed is the same as in the embodiment 1 and detailed description therefore is omitted.
Diagrams showing the adhesion of the toner to the surface of the development roller 3 during formation of a solid image are shown in
The relationship among the toner average toner particle diameter r, the development roller 3 surface roughness Rzjis (ten-point average roughness), and ghosting and fogging when images are formed on 10000 A4 size sheets by using the development device of this embodiment is shown in Table 1.
Ghosting occurred when the development roller 3 surface Rzjis is small because the toner fused onto the dielectric portions 31 and microfields were not formed by friction between the dielectric portions 31b and the toner. In contrast, when the development roller 3 surface Rzjis is increased, the dielectric portions 31b are charged to have the same polarity as the toner due to friction with the charging layer 41 and thus occurrence of toner fusion can be suppressed. As Rzjis increases, the ratio of the dielectric portions 31b charged to the same polarity as the toner increases, and the toner fusion can be significantly suppressed at Rzjis≧r (toner average particle diameter). The ratio of the dielectric portions 31b charged to have the same polarity as the toner is determined by Rzjis and the particle size distribution of the toner. The reason why fogging occurs when Rzjis>3r is that three layers of the toner are readily formed on the irregularities on the surface of the development roller 3 and the layer sandwiched between the toner and the toner cannot be charged. Accordingly, in order to suppress fogging, Rzjis≦3r is preferably satisfied.
In sum, the image forming apparatus of this embodiment includes a development roller 3 having dielectric portions 31 scattered on the surface, and the components are configured such that the position of the dielectric portions 31 in the triboelectric series is on the same polarity side, relative to the regulating blade 4, as the normal charge polarity of the toner. In this manner, an image forming apparatus that uses a development device having no developer supply member, suppresses the decrease in density at the back end of the solid image and ghosting, and is capable of realizing long life can be provided.
In this embodiment, the above-described method is employed to form surface roughness on the development roller 3 but the effects of the present invention are not limited to this as long as a method with which a particular surface roughness is obtained is employed and the dielectric portions 31b are protruded. For example, a conductive substrate may be coated with a surface layer composed of a conductive resin in which insulating particles are dispersed and the surface may be polished to make the insulating particles protrude so as to achieve a particular surface roughness. In this manner the same effects as the present embodiment can be achieved.
Next, another embodiment of the image forming apparatus according to the present invention is described.
In this embodiment, a developer in which an external additive 51 is scattered onto the surface of the toner 5 shown in
In this embodiment, a developer was prepared by using titanium oxide as the external additive and treating the toner surface by rapidly stirring 0.5 parts by mass of the external additive relative to 100 parts by mass of the toner. Although the detailed description is provided below, the development system of this embodiment utilizes the relationship of the work functions of the dielectric portions 31 on the surface of the development roller 3, the toner 5, and the external additive 51. The work functions of the toner 5 and the external additive 51 were 6.01 eV and 5.41 eV when measured by the aforementioned method.
In this embodiment, the materials for the toner 5 and the external additive 51 are selected so that the above-described work functions are satisfied and the order of the triboelectric series is (−) toner 5<dielectric portions 31<charging layer 41<external additive 51 (+). Furthermore, the difference in work function between the toner 5 and the dielectric portions 31 is adjusted to be smaller than the difference between the dielectric portions 31 and the external additive 51, and the difference in work function between the toner 5 and the charging layer 41 is adjusted to be greater than the difference between the charging layer 41 and the external additive 51. According to this structure, the toner 5 is negatively charged and the external additive 51 is positively charged due to the friction between the toner 5 and the dielectric portions 31, and the dielectric portions 31 are negatively charged due to the friction with the external additive 51 having a greater work function difference. Moreover, due to the friction between the toner 5 and the charging layer 41 and due to the friction with the toner 5 having a greater difference in work function, the charging layer 41 is positively charged.
The ghost image suppressing mechanism of this embodiment is described. This embodiment differs from the embodiment 1 in that the dielectric portions 31 are negatively charged. Since attraction of the toner to the surface of the development roller 3 in this invention is due to gradient force of the microfields, the direction of the force the toner receives is the direction in which the magnitude of the electric field increases irrespective of the direction of the electric field. Accordingly, as shown in
In other words, in this embodiment, because of the ghost image suppressing mechanism, occurrence of ghost images can be suppressed by making the toner coat amount after passage of the regulating position the same between during formation of the solid image and during formation of the solid white image. The results of forming images on 10000 A4 size sheets by using the development device of this embodiment and the development device of the embodiment 1 in the image forming apparatus shown in
Ghosting occurred as the number of sheets on which images were formed increased in the embodiment 1 because the toner fused onto the dielectric portions 31 and microfields could not be formed by the friction between the dielectric portions 31 and the toner. In contrast, in the embodiment 3, since the dielectric portions 31 has the same polarity as the toner, occurrence of the toner fusion was reduced and a long life can be realized.
As described above, the image forming apparatus of this embodiment includes a development roller 3 having dielectric portions 31 scattered on the surface and other components are configured so that, in a triboelectric series, the position of the dielectric portions 31 is on the same polarity, relative to the regulating blade 4, side as the normal charge polarity of the toner. In this manner, an image forming apparatus that includes a development device having no developer supply member, suppresses the decrease in density at the back end of a solid image, and suppresses occurrence of ghosting can be provided.
In this embodiment, the materials for the toner 5, the dielectric portions 31, and the charging layer 41 are as described above but are not limited to these. For example, when the toner is positively charged, the materials may be selected so that (−) external additive 51<charging layer 41<dielectric portions 31<toner 5 (+) so that the potential relationship among the conductive portions 32, the dielectric portions 31, and the charging layer 41 is as shown in
This embodiment is configured so that the triboelectric series is (−) toner 5<dielectric portions 31<charging layer 41<external additive 51 (+) but the triboelectric series may be (−) toner 5<dielectric portions 31<external additive 51<charging layer 41 (+) instead. In such a case, the difference in work function between the toner 5 and the dielectric portions 31 is adjusted to be smaller than the difference in work function between the dielectric portions 31 and the external additive 51 so that the dielectric portions 31 can be charged to the same polarity as the toner and the same effects as those of this embodiment can be achieved.
In this embodiment, titanium oxide is employed as the external additive 51. However, the external additive 51 may be any inorganic powder having the position in the triboelectric series described above among known inorganic powders described below. In particular, oxides of metals such as magnesium, zinc, and aluminum, complex metal oxide such as calcium titanate, and metal salts such as calcium carbonate that satisfy the position in the triboelectric series described above can be used.
Next, another embodiment of the image forming apparatus according to the present invention is described.
In this embodiment, the charging layer 41 of the regulating blade 4 is removed from the image forming apparatus described in the embodiment 1 and a blade bias Vbr is applied to a regulating blade 4b from a DC power source 72 (voltage applying apparatus) as shown in
In this embodiment, an electric field that removes the toner from the dielectric portions 31 is formed by the blade bias. A DC power source 71 for applying the development bias Vdc is connected to the development roller 3. Other main structures are the same as the embodiment 1.
The potential difference (Vmf hereinafter) between the dielectric portions 31 and the conductive portions 32 during formation of images was measured according to the following procedure:
In this embodiment, the value measured in (2) is 20 V. The acrylic resin particles of the dielectric portions 31 employed in this embodiment is dielectric constant=3.5 and resistivity=1E+15(Ω·m). Since the potential attenuation is 6%, Vmf=21.3 V during formation of images.
The results of forming images by applying a blade bias in this embodiment are shown in Table 3. Since a negatively charged toner is used in this embodiment, the potential difference (Vbr−Vdc) between the blade bias Vbr and the development bias Vdc is set to a positive value. In this manner, an electric field is generated in direction that causes the toner to move from the development roller 3 surface toward the regulating blade 4b.
Ghost images are suppressed by changing the potential difference (Vbr−Vdc) from minus to plus as shown in Table 3. The mechanism with which ghost images are suppressed is the same as the embodiment 1, i.e., the upper layer toner shown in
A potential graph of the conductive portions 32, the dielectric portions 31, and the regulating blade 4 of this embodiment is shown in
The potentials of the conductive portions 32, the dielectric portions 31, and the regulating blade 4 were set as shown in
As described above, the image forming apparatus of this embodiment includes a development roller 3 having dielectric portions 31 scattered on the surface and a voltage is applied to the regulating blade 4b so that the difference in potential obtained by subtracting the potential of the dielectric portions 31 from the potential of the regulating blade 4b has a polarity opposite to the normal charge polarity of the toner. In this manner, an image forming apparatus that includes a development device having no developer supply member, suppresses the decrease in density at the back end of a solid image, and suppresses occurrence of ghosting can be provided.
Next, another embodiment of the image forming apparatus according to the present invention is described.
In this embodiment, the charging layer 41 of the regulating blade 4 is removed from the image forming apparatus described in the embodiment 2 and a blade bias Vbr is applied to the regulating blade 4b from the DC power source 72 as shown in
The results of forming images by applying a blade bias in the present embodiment are shown in Table 4. Since a negatively charged toner is used in this embodiment, the potential difference (Vbr−Vdc) between the blade bias Vbr and the development bias Vdc is set to a positive value. As a result, an electric field is generated in the direction that causes the toner to move from the development roller 3 surface to the regulating blade 4b. In this embodiment, the surface roughness of the development roller 3 is Rzjis=6 μm and the toner average particle diameter is 6 μm. In this embodiment, Vmf=21.3 V as in the embodiment 4.
Ghost images are suppressed by changing the potential difference (Vbr−Vdc) from minus to plus as shown in Table 4. The mechanism with which ghost images are suppressed is the same as in the embodiment 3, i.e., the upper layer toner shown in
In this embodiment, when the development roller 3 surface roughness Rzjis of 17 μm and a toner average particle diameter of 6 μm were employed, all of the dielectric portions 31 were negatively charged and thus ghost images did not occur at a potential difference (Vbr−Vdc)>0. In this embodiment, the selection of the blade bias may be appropriately determined on the basis of the Rzjis, the average toner particle diameter, the particle size distribution, etc. As for the potential graph of this embodiment,
The mechanism with which the fusion of the toner onto the dielectric portions 31 is suppressed with the increase in number of sheets on which images are formed is the same as that of the embodiment 3.
The development device shown in
As discussed above, the image forming apparatus of this embodiment includes a development roller 3 having dielectric portions 31 scattered on the surface and a voltage is applied to the regulating blade 4b so that the potential difference determined by subtracting the potential of the dielectric portions 31 from the potential of the regulating blade 4b is controlled to have a polarity opposite to the normal charge polarity of the toner. In this manner, an image forming apparatus that uses a development device having no developer supply member, suppresses the decrease in density at the back end of the solid image and ghosting, and is capable of realizing long life can be provided.
Next, another embodiment of the image forming apparatus according to the present invention is described.
In this embodiment, the charging layer 41 of the regulating blade 4 is removed from the image forming apparatus described in the embodiment 3 and a blade bias is applied to the regulating blade 4b as shown in
The results of forming images by applying the blade bias in this embodiment are shown in Table 5. Since a negatively charged toner is used in this embodiment, the potential difference (Vbr−Vdc) is set so that the (Vbr−Vdc) between the blade bias Vbr and the development bias Vdc is a positive value. In this manner, an electric field is generated in a direction that causes the toner to move from the development roller 3 surface to the regulating blade 4b.
As shown in Table 5, ghost images are suppressed by changing the potential difference (Vbr−Vdc) from minus to plus. The mechanism with which ghost images are suppressed is the same as in the embodiment 2, i.e., the upper layer toner shown in
Here, the potential graph of the conductive portions 32, the dielectric portions 31, and the regulating blade 4b of this embodiment is shown in
The mechanism with which the fusion of the toner onto the dielectric portions 31 caused by the increase in the number of sheets on which the images are formed is suppressed is the same as that of the embodiment 2.
The potentials of the conductive portions 32, the dielectric portions 31, and the regulating blade 4 were set as shown in
As described above, the image forming apparatus of this embodiment includes a development roller 3 having dielectric portions 31 scattered on the surface and a voltage is applied to the regulating blade 4b so that the difference in potential obtained by subtracting the potential of the dielectric portions 31 from the potential of the regulating blade 4b has a polarity opposite to the normal charge polarity of the toner. In this manner, an image forming apparatus that includes a development device having no developer supply member, suppresses the decrease in density at the back end of a solid image, and suppresses occurrence of ghosting can be provided.
As discussed above, according to the present invention, the decrease in density at the back end of a solid image and occurrence of ghosting can be suppressed with a development device that has no toner supply member that contacts the toner bearing member and supplies and removes the toner.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of International Patent Application No. PCT/JP2012/054799, filed Feb. 27, 2012, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/JP2012/054799 | Feb 2012 | JP | national |
