JP2007121857A - Image forming apparatus and imaging forming process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce uneven charging of a photoreceptor due to the variance of a gap between the photoreceptor and a charging roller without costs while suppressing deterioration of the photoreceptor and the charging roller. <P>SOLUTION: In an image forming apparatus wherein an AC voltage having a DC current superposed thereon is applied to the photoreceptor and the charging roller disposed in non-contact with the photoreceptor, to perform a charging process, circumferential deflection in an image forming region of the photoreceptor is 4 to 100 μm, and a plurality of continuous steps which have height differences of 2 to 30 μm and have lengths of ≥400 μm are formed on the surface of the charging roller, and a longitudinal center axial line (longitudinal direction) of the charging roller is taken as an X axis in order to extract the continuous steps into an XP plane, and 10 or more distances Yn from the X axis, of arbitrary X (Xn) are plotted at arbitrary distance, and a correlation coefficient and an inclination resulting from linearly approximating the steps by the method of least squares are ≤0.9, and -0.5 to 0.5 respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a fax machine, or a multifunction machine having these functions, and a process cartridge, and more particularly to an optimum gap between an image carrier and a charging roller for efficient charging. It is related to evaluation and judgment to decide. The process cartridge refers to a cartridge in which at least the image carrier and the charging unit are integrally formed into a cartridge that can be attached to and detached from the image forming apparatus main body.

JP 2000-75701 A JP 2004-264792 A JP 2002-108059 A JP-A-2005-4000

  In an image forming apparatus using an electrophotographic process, image formation is performed by subjecting a photoreceptor to a charging step, an exposure step, a development step, a transfer step, and a fixing step. For the charging process, scorotron chargers have been used in the past. However, due to environmental problems, generation of harmful gases such as ozone and NOx is small, and a charging roller that can reduce the size of the device has recently been used as a charger. It is becoming. In the charging mechanism when the charging roller is used for charging, discharge does not occur if the distance between the photosensitive member and the charging roller is too narrow, and according to Paschen's law, the gap is 8 μm, and discharge does not occur below that. Absent. Actually, since there are capacitive components of the charging roller and the photosensitive member, discharge starts at 20 μm or more, and when the gap is 20 μm or more, the discharge density decreases as the gap increases.

  When the resistance of the charging roller is partially uneven, the charge is concentrated on a portion having a low resistance value, and an excessive current flows locally to cause charging unevenness. Therefore, uniformity of resistance is desired. Further, regarding the unevenness on the surface of the charging roller, it is desired that the surface roughness is small because discharge tends to concentrate on the convex portion. In so-called contact charging in which the photosensitive member and the charging roller are used in contact with each other, discharge occurs when the gap in the region slightly outside the nip becomes 20 μm or more. When charging is performed by applying a DC voltage to the charging roller, the chance of discharging from each point on the charging roller to the photosensitive member in order to charge the photosensitive member to a predetermined potential is the moment when it passes through the gap width according to Paschen's law. Therefore, there has been a demand for a smooth charging roller capable of keeping the relative position of the charging roller and the photosensitive member constant. When an AC voltage is superimposed on a DC voltage and applied to the charging roller during charging, positive and negative discharges are repeated according to the frequency, and therefore it is not always necessary that the charging roller surface has a smooth shape.

  In Patent Document 1, in an image forming apparatus that performs contact charging, if irregularities exist between the photoconductor and the charging roller, a minute space is formed in the nip and discharge occurs. It is being considered to apply. However, if the surface of the charging roller has large irregularities, the photoconductor and the charging roller are in contact with each other, so the photoconductor may be damaged. Considering that, the charging roller is preferably smooth. When image formation is performed while the charging roller is in contact with the photoconductor, if the residual toner after transfer cannot be completely cleaned, the residual toner adheres to the charging roller, causing variations in the resistance of the charging roller, and charging the photoconductor. As a result, the potential varies and causes uneven image density. Therefore, so-called non-contact charging in which a gap is provided between the photosensitive member and the charging roller to charge the photosensitive member has been proposed (for example, Patent Document 2, Patent Document 3, and Patent Document 4). As described above, since the density of discharge varies depending on the size of the gap, it is necessary to control the gap between the photosensitive member and the charging roller in non-contact charging. Conventionally, in the non-contact charging, the charging roller has to be controlled. A smooth surface shape has been considered ideal. In this charging step, the photoconductor can be set to a target voltage by applying an alternating voltage in a superimposed manner. The charging parameters at this time include the AC voltage and frequency to be applied, the resistance (resistance unevenness) of the charging roller, the resistance of the photosensitive member (resistance unevenness), the gap between the photosensitive member and the charging roller, and the gap variation. When there is gap variation, the discharge density changes depending on the gap, and charging unevenness occurs.

  Causes of gap variation include dimensional accuracy and assembly accuracy of the photoconductor and charging roller, and vibration (shake) of the photoconductor / charging roller. Among these, the dimensional accuracy of the photoconductor and the charging roller can be increased to an accuracy that does not hinder gap variation by making the manufacturing conditions appropriate. In particular, it is possible to reduce the coating unevenness to several μm or less by examining the conditions of the dip coating. As for the assembly accuracy, it is possible to increase the accuracy to such an extent that variations in the discharge density do not become a problem by increasing the strength of the spring and the accuracy of the charging roller or the photoreceptor support member. On the other hand, it is very difficult to reduce the vibration (shake) of the photoconductor. In other words, in order to suppress the vibration (vibration) of the photosensitive member, the photosensitive element tube is formed of a metal cylinder. Therefore, the thickness of the cylindrical element tube such as aluminum is increased, and the accuracy of the cylindrical element tube and the flange is increased. It is necessary to increase the assembling accuracy of the cylindrical raw tube and the flange. However, since the cost of the elementary tube in the photoconductor is very high, it is not possible to use a thick tube for the photoconductor. In general, the flange is plastic, the photoconductor is metal, and the flange is press-fitted into a cylindrical tube. Therefore, there is a limit to the accuracy with which the photoconductor drum and the flange can be assembled. It can only be of a certain level. In particular, it is possible to minimize the shake by selecting only those with a small shake or by using a metal flange, but the cost of the photoconductor becomes very high by such a method. It is theoretically possible to make the charging potential of the photosensitive member uniform by increasing the frequency of the current applied to the charging roller when charging the photosensitive member with shake, and increasing the discharge frequency. However, if the frequency is increased too much, the speed of deterioration of the photosensitive member and the charging roller increases, and there is a demand for setting the frequency as low as possible. In this case, the charging roller also shakes, but since the charging roller is made of a cylindrical metal having a small outer diameter, the touch of the charging roller can be ignored.

  As described above, in order to prevent charging unevenness as much as possible, the cause of gap variation between the charging roller and the photosensitive member is suppressed (the dimensional accuracy and assembling accuracy of the photosensitive member and the charging roller are increased, and vibration (sway) It is important to reduce), but the prior art was expensive.

  SUMMARY OF THE INVENTION An object of the present invention is to reduce the uneven charging of a photoconductor due to a gap variation between the photoconductor and the charging roller without increasing the cost while suppressing deterioration of the photoconductor and the charging roller.

  The present inventors have found that when using a photoconductor with low cost and slight fluctuation, the unevenness of discharge due to the change in the gap between the photoconductor and the charging roller, and the resulting nonuniform charging of the photoconductor, As a result of observing in detail the gap variation between the photoconductor and the charging roller, how to solve it without shortening the service life, the photoconductor does not vibrate finely, but gently shakes like a precession. For this reason, if the charging roller is uniform, the gap fluctuates slowly, and charging unevenness is likely to occur slowly and periodically, and the resulting image density unevenness is easily recognized by the human eye. It turns out that it is a thing. As described above, since it is practically difficult to suppress the shake of the photoconductor due to the cost of the photoconductor, the present inventors have investigated whether the gap unevenness can be solved by the shape of the charging roller. It has been found that if the roller is provided with many fine steps in the longitudinal direction of the charging roller, unevenness due to the shake of the photoreceptor can be absorbed to some extent. However, if the steps are perfectly aligned in the longitudinal direction of the charging roller, periodicity will occur in the charging unevenness that runs in the lateral direction of the image, so that the steps run in the longitudinal direction but meandering. As a result, the present inventors have found that the present invention is preferable.

  That is, the present invention relates to an image forming apparatus in which a charging process is performed by applying an alternating voltage on which a direct current is superimposed on a photosensitive member (image carrier) and a charging roller disposed in non-contact with the photosensitive member. In order to extract the continuous step on the XY plane, the circumferential runout in the image forming area of the body is 4 to 100 μm, and the surface of the charging roller has a plurality of steps that are 2 to 30 μm in height and 400 μm in length. When the vertical center axis (longitudinal direction) of the charging roller is the X axis, the distance Yn from the X axis at an arbitrary X (Xn) is plotted at 10 or more points at an arbitrary interval, and the step is approximated by a least square method. An image forming apparatus having a correlation coefficient of 0.9 or less and a slope of −0.5 to 0.5.

  According to the present invention, it is possible to provide an image forming apparatus capable of forming a high-quality image without charging unevenness, and having a low oxidative deterioration of a photoconductor and a charging roller and a low replacement frequency. According to the second aspect of the present invention, it is possible to avoid the occurrence of an abnormal image due to the remaining toner sandwiched between the image carrier / photosensitive member and the charging roller. According to the invention described in claim 3 or 4, strict evaluation is possible. According to the invention described in claim 5, a high-resolution image can be formed.

  The gap between the image forming area of the charging roller and the image carrier / photoreceptor used in the present invention is an average of 10 to 150 μm, preferably 14 to 100 μm, more preferably 18 to 60 μm when the photoconductor and the charging roller are stationary. It is. If the average gap between the photosensitive member and the charging roller is less than 10 μm, the toner that has not been cleaned due to the proximity of the photosensitive member and the charging roller is caught between the photosensitive member and the charging roller, and a streak-like abnormal image is likely to occur. This is not preferable. When the average gap between the photosensitive member and the charging roller exceeds 150 μm, it is necessary to increase the AC voltage applied to the charging roller in order to generate discharge. If it is too large, the amount of ozone generated is large. This is not preferable.

  The circumferential runout in the image forming area of the photoreceptor used in the present invention is 4 to 100 μm, preferably 7 to 70 μm, and more preferably 8 to 30 μm. If the circumferential runout of the photoconductor is less than 4 μm, it is not preferable because the manufacturing cost of the photoconductor will be very high with accuracy. This is not preferable because the photosensitive member and the charging roller are too close to each other and the toner that cannot be cleaned due to the proximity of the photosensitive member and the charging roller is caught between the photosensitive member and the charging roller, and a streak-like abnormal image is likely to occur. . In the present invention, “circumferential runout” refers to the definition of “radial runout in the radial direction” of JIS B 0621, and the runout in the image forming area of the photoconductor is measured and set to the largest value. However, in general, the shake of the photoconductor tends to increase as it approaches the both end portions. Therefore, two points (X, X, 30 mm) from both ends of the photoconductor (both ends do not include the flange portion and both ends of the base tube). Y: Measurement may be performed on FIG. 7, and the larger value when comparing “circumferential runout in the radial direction” at two points (X, Y) may be adopted. For the measurement of circumferential runout, the surface of the photoreceptor was measured using a non-contact dimension measuring device (manufactured by Mitutoyo Corporation, laser scan micrometer). The measurement was performed with the flange assembled to the photoreceptor.

  The surface of the charging roller used in the present invention has a plurality of steps, and the height difference of the steps is 2 to 30 μm, preferably 3 to 20 μm, more preferably 4 to 15 μm. If the level difference is less than 2 μm, the effect of reducing the gap variation does not appear. Therefore, if the level difference exceeds 30 μm, the most concave portion of the charging roller level difference is too far from the photoconductor to make it difficult to discharge. In order to cause discharge also in that portion, it is necessary to increase the AC voltage applied to the charging roller. If it is too large, the amount of ozone generated increases, which is not preferable.

  The step of the charging roller used in the present invention has a width having a step difference of 10 μm or less, preferably 5 μm or less, more preferably 0.1 to 3 μm, and a height difference of 2 to 30 μm. It is preferable. The step is continuously present over a length of at least 100 μm, preferably 400 μm. The function of absorbing and mitigating periodic charging unevenness that occurs and is easily recognized by the human eye depends on the linearity and inclination of successive steps, so the linearity and inclination must be specified. . The step is extracted on the XY plane with the longitudinal direction of the charging roller as the X-axis direction, and the distance Yn from the X-axis at any X (Xn) is sampled and plotted at an interval such that the number of sampling points is 10 or more. The correlation coefficient and the slope when the step is linearly approximated by the least square method are defined. Since the level difference at which the sampling is performed is as large as 2 μm or more, it can be easily identified as a line in an electron microscope image or an optical image of 30 to 1000 times.

  When a set of plot points when extracting successive steps on the XY plane is a perfect straight line, periodic unevenness that can be easily recognized by the human eye is likely. The degree of meandering is such that the correlation coefficient when plot points are linearly approximated by the least square method is 0.9 or less (other than 0), preferably 0.4 or less (other than 0), more preferably 0.1 or less (0 Except). When the correlation coefficient exceeds 0.9, the linearity is too high, and it is not preferable because it does not contribute to the reduction of periodic unevenness.

  Even when all the meander lines extracted on the XY plane extend without an angle in the longitudinal direction, periodic unevenness that is easily recognized by the human eye is likely to occur. The degree of the inclination is −0.5 to 0.5, preferably −0.3 to 0.3, more preferably −0.1 when the step is linearly approximated by the least square method. -0.1 is good. When the inclination is less than −0.5 or exceeds 0.5, it is not preferable because unevenness in the circumferential direction is likely to occur.

  In the present invention, high-quality image formation is possible in both monochrome image formation and color image formation, but the effect is particularly high in color image formation that requires high-quality image formation. While doing so, the life of the photoreceptor and the charging roller can be greatly extended. When the present invention is capable of forming a color image, a single photoconductor is used, and after developing the toner of each color on the photoconductor, the toner image on the photoconductor of each color is sequentially transferred to the intermediate transfer member or the image carrier. A method for forming an image, a method in which a photosensitive member is used for the number of toner colors, each color toner is developed on a separate photosensitive member, and transferred to an intermediate transfer member or an image carrier (tandem type or the like). ) Both have excellent performance. In the tandem type, it is necessary to take a charging step with a charging roller in order to suppress the generation of an oxidizing gas such as ozone accompanying charging, but the charging step used in the present invention has gentle charging conditions. The amount of oxidizing gas generated is particularly small. Therefore, the present invention is not only capable of forming a high-quality and highly reliable image, but is also environmentally friendly.

The charging process and the step shape related to the present invention will be described in more detail with reference to the drawings.
FIG. 1 schematically shows an image forming apparatus according to the present invention. The image forming apparatus shown here is configured as a copying machine, a printer, a facsimile, or a multifunction machine having at least two of these functions. A photoreceptor 1 as an example of a member to be charged is disposed in a main body housing (not shown), and the photoreceptor 1 is configured by laminating a photosensitive layer 3 on the outer peripheral surface of a conductive base 2 on a drum. Yes. It is also possible to use a belt-like photoreceptor that is wound and driven around a plurality of rollers, or a drum-like or belt-like photoreceptor made of a dielectric. In the present embodiment, at least the photosensitive member 1 and the charging device 5 constitute a process cartridge unit, and a developing device, a cleaning unit, and a charge removal device can be further added to constitute a process cartridge. When referred to as a process cartridge, the cartridge unit alone can be a process cartridge, and there can be various variations such as a charging device, a photosensitive member, a developing device, a charging device, a photosensitive member, a developing device, and a cleaning device.

  During the image forming operation, the photosensitive member 1 is rotationally driven in the clockwise direction in FIG. 1, and the surface thereof moves in the arrow A direction. At this time, the surface of the photosensitive member is irradiated with light from the static elimination lamp 4, the surface is initialized, and then the surface of the photosensitive member is charged to a predetermined polarity by the charging device 5 (the charging device 5 will be described in detail later). . The surface of the photosensitive member charged by the charging device 5 is irradiated with light-modulated laser light emitted from a laser writing unit 6 which is an example of an exposure device, thereby forming an electrostatic latent image on the surface of the photosensitive member. The Next, when the electrostatic latent image passes through the developing device 7, it is visualized as a toner image by toner charged to a predetermined polarity.

  On the other hand, a transfer material P (paper) is fed between the photoconductor 1 and the transfer device 8 opposed to the photoconductor 1 at a predetermined timing. At this time, a toner image formed on the photoconductor is transferred onto the transfer material P. Is electrostatically transferred to. The transfer material P to which the toner image has been transferred subsequently passes between the fixing roller 10 and the pressure roller 11 of the fixing device 9, and the toner image is fixed on the transfer material by the action of heat and pressure. The The transfer residual toner that is not transferred to the transfer material and remains on the surface of the photoreceptor is removed by the cleaning device 12.

  The charging device 5 includes a charging roller 13 disposed to face a surface of a charged object to be moved, in the illustrated example, the surface of the photosensitive member 1, and a power source 14 that applies a voltage to the charging roller 13. A voltage is applied to the charging roller 13 by the power source 14 to generate a discharge between the charging roller 13 and the surface of the photoconductor to charge the surface of the photoconductor with a predetermined polarity.

  The charging roller 13 shown in FIG. 1 is formed in a cylindrical shape, and the whole can be made of a metal such as stainless steel. However, since the photosensitive member may be damaged due to contact with the photosensitive member when the charging roller is assembled, a structure in which rubber or plastic material is coated on the outside of the cylindrical metal is used.

  The charging roller 13 shown in FIG. 1 is non-contact with the surface of the photosensitive member, and the gap between the photosensitive member and the charging roller is 10 to 150 μm on average, preferably 14 to 100 μm, more preferably 18 to 60 μm. ing. If the average gap between the photosensitive member and the charging roller is less than 10 μm, the toner that has not been cleaned due to the proximity of the photosensitive member and the charging roller is caught between the photosensitive member and the charging roller, and a streak-like abnormal image is likely to occur. Therefore, it is not preferable. In addition, when the average gap between the photosensitive member and the charging roller exceeds 150 μm, it is necessary to increase the AC voltage applied to the charging roller in order to generate discharge. Is unfavorable because of an increase in the amount of.

  FIG. 2 shows an example of a configuration for causing the charging roller 13 to face each other with a minute gap G from the surface of the photoreceptor. The charging roller 13 shown here has a spacer made of a tape 20 attached to each end region in the longitudinal direction. The tape 20 comes into contact with the surface of the photosensitive member so that the charging roller 13 is brought into contact with the surface of the photosensitive member. On the other hand, the minute gap G is maintained. In addition, a minute gap can be secured using a flange or the like.

  An electron micrograph of an example of the charging roller 13 used in the present invention is shown in FIG. The direction of the white arrow represents the longitudinal direction of the charging roller. In FIG. 3, continuous steps are observed as streaks. The streaks corresponding to the steps are meandering continuous lines having a thickness of about 1 μm, and there are a plurality of lines in the longitudinal direction of the charging roller (X-axis direction). Since the step is meandering instead of a straight line, periodic charging unevenness expected when the step is a straight line can be effectively reduced. In addition, since a plurality of continuous steps are not parallel to each other and each has an inclination with respect to the X-axis direction, the unevenness of the horizontal stripes that is expected when all the continuous steps are in the X-axis direction is almost generated. Absent. Since the level difference is as large as 2 μm or more, it can be easily identified as a line on an electron microscope image or an optical image of 30 to 1000 times, preferably 30 to 100 times. If it is less than 30 times, it is not preferable because the resolution is low and it becomes impossible to discriminate stripes. If it exceeds 1000 times, it is not preferable because it is difficult to sample a continuous step of 400 μm or more. However, it is important to check the size of the step with a three-dimensional SEM, laser microscope, tunnel microscope, etc., and to extract only the step of 2 μm or more, because it can be confirmed even with a small step difference in elevation due to advances in the microscope.

A step line of 2 μm or more is extracted on the XY plane from the electron micrograph of FIG. 3 and shown in FIG. All the steps extracted here were confirmed to have a height difference of 2 μm or more by three-dimensional SEM. Each extracted step line is defined as step 1, step 2, step 3, step 4 from the top, and each line is sampled at an arbitrary interval, linear approximation is performed using the least square method, and the slope and correlation coefficient. Ask for. The sampling number is 10 points or more, preferably 15 points or more, and more preferably 20 to 100 points. The more the number of samples on a single step line, the more accurate linear regression can be performed.However, if the number of samplings exceeds a certain level, the linearly regressed line hardly changes. As an example of regression, a method for obtaining the slope and correlation coefficient for the step 1 will be described. When the step 1 was extracted by 1000 μm and 166 points were sampled and linear approximation was performed using the least square method, a correlation coefficient of 0.53 and a slope of −0.13 were obtained (FIG. 5). Similarly, the slope and the correlation coefficient are derived for the steps 2 to 4, and the correlation coefficient 0.44 and the slope −0.07 for the step 2 and the correlation coefficient 0.07 and the slope for the step 3, respectively. A correlation coefficient of 0.73 and a slope of 0.40 were obtained for 0.03, level difference 4. In the step relating to the present invention, it is preferable to perform linear regression on all the steps existing on the surface of the charging roller ideally, but the area of the surface of the charging roller is 0.36 to ⁴ mm ² , preferably 0.49 to ² mm ² . It is enough to ask for the part. In consideration of variations due to the location of the charging roller, the step in the above-mentioned area is analyzed for one end or both ends of the center and the portion corresponding to the image forming area, and 85% or more, preferably 90% or more of the step. Is a step with a height difference of 2 to 30 μm and a length of 400 μm or more. The step is extracted on the XY plane with the longitudinal direction of the charging roller as the X axis, and is obtained by plotting 10 or more points at arbitrary intervals. It is preferable that the correlation coefficient when the line is linearly approximated by the method of least squares is 0.9 or less and the slope is −0.5 to 0.5.

  As a method for creating an effective step on the surface of the charging roller, mechanical grinding or a drawing means method, a method using volume change during the production of the resin used for the charging roller, an inner surface of all molds in the molding process in advance. There is a method of forming a step. Among them, the method of providing a step on the inner surface in advance in the molding process is preferable because the entire shape to be poured is constant, and a preferable surface shape can be produced with good reproducibility when producing a large number of charging rollers.

  The layer structure of the charging roller used in the present invention is preferably configured to have a polymer layer and a surface layer on a conductive support. The conductive support functions as an electrode and a support member for the charging roller. For example, a metal or alloy such as aluminum, copper alloy, stainless steel, iron plated with chromium, nickel, or the like, resin of a conductive agent It is made of a conductive material such as.

The polymer layer is preferably a conductive layer having a resistance of 10 ⁶ to 10 ⁹ Ωcm, and a polymer material mixed with a conductive material to adjust the resistance is used. As the polymer of the polymer layer of the charging roller, styrenic resins such as polyester-based, olefin-based thermoplastic elastomer, polystyrene, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, etc. Thermoplastic resin, isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, urethane rubber, silicone rubber, fluoro rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide- Allyl glycidyl ether copolymer rubber, ethylene-propylene-diene terpolymer rubber (EPDM), acrylonitrile-butadiene copolymer rubber, natural rubber, etc. And rubber material obtained by blending thereof. Among the rubber materials, silicone rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, acrylonitrile-butadiene copolymer rubber and blended rubber thereof are preferably used. These rubber materials may be foamed or non-foamed.

  As the conductive agent, an electronic conductive agent or an ionic conductive agent is used. Examples of electronic conductive agents include carbon blacks such as ketjen black and acetylene black; pyrolytic carbon, graphite; various conductive metals or alloys such as aluminum, copper, nickel, and stainless steel; tin oxide, indium oxide, titanium oxide Examples thereof include various conductive metal oxides such as tin oxide-antimony oxide solid solution and tin oxide-indium oxide solid solution; those obtained by conducting the surface of an insulating material; Examples of ionic conductive agents include perchlorates and chlorates such as tetraethylammonium and lauryltrimethylammonium; alkali metals such as lithium and magnesium; perchlorates and chlorates of alkaline earth metals Can be mentioned. These conductive agents may be used alone or in combination of two or more. Moreover, the addition amount is not particularly limited, but in the case of the electronic conductive agent, it is preferably in the range of 1 to 30 parts by mass with respect to 100 parts by mass of the polymer, and in the range of 15 to 25 parts by mass. More preferably. On the other hand, in the case of the ionic conductive agent, it is preferably in the range of 0.1 to 5.0 parts by mass, and in the range of 0.5 to 3.0 parts by mass with respect to 100 parts by mass of the polymer. Is more preferable.

  The polymer material constituting the surface layer is not particularly limited as long as the dynamic ultra-small hardness on the surface of the charging roller is 0.04 or more and 0.5 or less, but polyamide, polyurethane, polyvinylidene fluoride, tetrafluoroethylene Copolymer, polyester, polyimide, silicone resin, acrylic resin, polyvinyl butyral, ethylene tetrafluoroethylene copolymer, melamine resin, fluoro rubber, epoxy resin, polycarbonate, polyvinyl alcohol, cellulose, polyvinylidene chloride, polyvinyl chloride, polyethylene And ethylene vinyl acetate copolymer. Among these, polyamide, polyvinylidene fluoride, tetrafluoroethylene copolymer, polyester, and polyimide are preferably used from the viewpoint of releasability with toner and the like. The above polymer materials may be used alone or in combination of two or more. Further, the number average molecular weight of the polymer material is preferably in the range of 1000 to 100,000, and more preferably in the range of 10,000 to 50,000.

  The surface layer is formed as a composition by mixing the polymer material with the conductive agent used in the conductive elastic layer and various fine particles. As the fine particles, metal oxides such as silicon oxide, aluminum oxide, and barium titanate and composite metal oxides, and polymer fine powders such as tetrafluoroethylene and vinylidene fluoride are used alone or in combination. It is not limited to. The surface layer has a thickness of 0.5 to 12 μm, preferably 1 to 10 μm, and more preferably 2 to 8 μm so as not to impair the shape of the step. If the surface layer is less than 0.5 μm, the layer is too thin, and a portion where the surface layer is not present locally and a portion where the surface layer is present are formed. If the surface layer exceeds 12 μm, the surface layer hides the step, and thus it becomes difficult to exert the function of reducing charging unevenness due to the presence of the step which is the object of the present invention.

  In the photoreceptor used in the present invention, a photosensitive layer is provided on a conductive support. The photosensitive layer is composed of a single layer type in which a charge generation material and a charge transport material are mixed, a forward layer type in which a charge transport layer is provided on the charge generation layer, or a charge generation layer on the charge transport layer. There is a reverse layer type provided. A protective layer can also be provided on the photosensitive layer. An undercoat layer may be provided between the photosensitive layer and the conductive support. If necessary, an appropriate amount of a plasticizer, an antioxidant, a leveling agent and the like can be added to each layer.

Examples of the conductive support for the photoreceptor include those having a volume resistance of 10 ¹⁰ Ωcm or less, for example, metals such as aluminum, nickel, chromium, nichrome, copper, gold, silver, platinum, tin oxide, indium oxide, etc. A metal or oxide film, or a film or cylindrical plastic or paper coated by vapor deposition or sputtering, or a plate made of aluminum, aluminum alloy, nickel, stainless steel, etc. After forming a blank, a tube that has been surface-treated by cutting, superfinishing, polishing, or the like can be used. As the drum-shaped support, those having a diameter of 20 to 150 mm, preferably 24 to 100 mm, and more preferably 28 to 70 mm can be used. If the diameter of the drum-shaped support is less than 20 mm, it is physically difficult to arrange means for performing charging, exposure, development, transfer, and cleaning steps around the drum, and the diameter of the drum-shaped support is 150 mm. If it exceeds, the image forming apparatus becomes large, which is not preferable. In particular, when the image forming apparatus is a tandem type, it is necessary to mount a plurality of photoconductors, and thus the diameter is preferably 70 mm or less, and preferably 60 mm or less. Further, endless nickel belts and endless stainless steel belts disclosed in JP-A-52-36016 can also be used as the conductive support.

  Examples of the undercoat layer of the photoreceptor used in the present invention include a resin or a material mainly composed of a white pigment and a resin, and a metal oxide film obtained by chemically or electrochemically oxidizing the surface of a conductive substrate. However, those containing a white pigment and a resin as main components are preferred. Examples of white pigments include metal oxides such as titanium oxide, aluminum oxide, zirconium oxide, and zinc oxide. Among them, it is most preferable to contain titanium oxide that is excellent in preventing charge injection from a conductive substrate. Examples of the resin used for the undercoat layer include thermoplastic resins such as polyamide, polyvinyl alcohol, casein, and methylcellulose; thermosetting resins such as acrylic, phenol, melamine, alkyd, unsaturated polyester, and epoxy; Various mixtures can be exemplified.

  Examples of the charge generating material for the photoreceptor used in the present invention include azo pigments such as monoazo pigments, bisazo pigments, trisazo pigments, tetrakisazo pigments, triarylmethane dyes, thiazine dyes, oxazine dyes, Xanthene dyes, cyanine dyes, styryl dyes, pyrylium dyes, quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, bisbenzimidazole pigments, indanthrone pigments, squarylium pigments, phthalocyanine Organic pigments and dyes such as pigments, and inorganic materials such as selenium, selenium-arsenic, selenium-tellurium, cadmium sulfide, zinc oxide, titanium oxide, amorphous silicon, etc. can be used. Can be used as a mixture.

  Examples of the charge transport material for the photoreceptor used in the present invention include anthracene derivatives, pyrene derivatives, carbazole derivatives, tetrazole derivatives, metallocene derivatives, phenothiazine derivatives, pyrazoline compounds, hydrazone compounds, styryl compounds, styrylhydrazone compounds, enamine compounds, A butadiene compound, distyryl compound, oxazole compound, oxadiazole compound, thiazole compound, imidazole compound, triphenylamine derivative, phenylenediamine derivative, aminostilbene derivative, triphenylmethane derivative, etc. it can.

  The binder resin used for forming the photosensitive layer of the charge generation layer and the charge transport layer is electrically insulating, and is a known thermoplastic resin, thermosetting resin, photocurable resin, and photoconductive material. Suitable binder resins include, for example, polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, Ethylene-vinyl acetate copolymer, polyvinyl butyral, polyvinyl acetal, polyester, phenoxy resin, (meth) acrylic resin, polystyrene, polycarbonate, polyarylate, thermoplastic resin such as polysulfone, polyethersulfone, ABS resin, phenol resin , Epoxy resin, urethane resin, melamine resin, isocyanate resin, alkyd tree In addition, a thermosetting resin such as a silicone resin and a thermosetting acrylic resin, a photoconductive resin such as polyvinyl carbazole, polyvinyl anthracene, and polyvinyl pyrene, or a mixture of various types of binder resins can be given. However, the present invention is not particularly limited to these.

As antioxidant, the following are used, for example.
[Monophenol compound]
2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, stearyl-β- (3,5-di-t-butyl-4 -Hydroxyphenyl) propionate, 3-t-butyl-4-hydroxynisol, etc. [bisphenol compounds]
2,2′-methylene-bis- (4-methyl-6-tert-butylphenol), 2,2′-methylene-bis- (4-ethyl-6-tert-butylphenol), 4,4′-thiobis- ( 3-methyl-6-tert-butylphenol), 4,4′-butylidenebis- (3-methyl-6-tert-butylphenol), etc. [polymeric phenol compound]
1,1,3-tris- (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t- Butyl-4-hydroxybenzyl) benzene, tetrakis- [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane, bis [3,3′-bis (4 ′) -Hydroxy-3'-t-butylphenyl) butyric acid] glycol ester, tocophenols, etc. [paraphenylenediamines]
N-phenyl-N'-isopropyl-p-phenylenediamine, N, N'-di-sec-butyl-p-phenylenediamine, N-phenyl-N-sec-butyl-p-phenylenediamine, N, N'- Di-isopropyl-p-phenylenediamine, N, N′-dimethyl-N, N′-di-t-butyl-p-phenylenediamine, etc. [hydroquinones]
2,5-di-t-octylhydroquinone, 2,6-didodecylhydroquinone, 2-dodecylhydroquinone, 2-dodecyl-5-chlorohydroquinone, 2-t-octyl-5-methylhydroquinone, 2- (2-octadecenyl) ) -5-Methylhydroquinone etc. [Organic sulfur compounds]
Dilauryl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, ditetradecyl-3,3′-thiodipropionate, etc. [Organic phosphorus compounds]
Triphenylphosphine, tri (nonylphenyl) phosphine, tri (dinonylphenyl) phosphine, tricresylphosphine, tri (2,4-dibutylphenoxy) phosphine and the like.

  As the plasticizer, those used as plasticizers for general resins such as dibutyl phthalate and dioctyl phthalate can be used as they are, and the amount used is about 0 to 30 parts by weight with respect to 100 parts by weight of the binder resin. Is appropriate.

  A leveling agent may be added to the charge transport layer. As the leveling agent, silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, and polymers or oligomers having a perfluoroalkyl group in the chain are used, and the amount used is 0 to 100 parts by weight of the binder resin. One part by weight is appropriate.

  The protective layer is a layer in which fine particles of metal or metal oxide are dispersed in a binder resin. As the binder resin, a resin that is transparent to visible and infrared light and excellent in electrical insulation, mechanical strength, and adhesiveness is desirable. As the binder resin of the protective layer, ABS resin, ACS resin, olefin-vinyl monomer copolymer, chlorinated polyether, allyl resin, phenol resin, polyacetal, polyamide, polyamideimide, polyacrylate, polyallylsulfone, polybutylene, Polybutylene terephthalate, polycarbonate, polyethersulfone, polyethylene, polyethylene terephthalate, polyimide, acrylic resin, polymethylbenten, polypropylene, polyphenylene oxide, polysulfone, polystyrene, AS resin, butadiene-styrene copolymer, polyurethane, polyvinyl chloride, poly Examples of the resin include vinylidene chloride and epoxy resin. Examples of the metal oxide include titanium oxide, tin oxide, potassium titanate, TiO, TiN, zinc oxide, indium oxide, and antimony oxide. In addition to the protective layer, fluorine resins such as polytetrafluoroethylene, silicone resins, and those obtained by dispersing other inorganic materials in these resins can be added for the purpose of improving wear resistance. As a method for forming the protective layer, a normal coating method is employed. In addition, about 0.1-10 micrometers is suitable for the thickness of a protective layer.

  Examples of the solvent used for producing the photoreceptor include chlorinated solvents such as dichloromethane, tetrahydrofuran, dioxane, toluene, cyclohexanone, methyl ethyl ketone, acetone and the like.

  At both ends of a photosensitive member provided with a photosensitive layer on a drum-shaped conductive support, flanges are usually provided for supporting the photosensitive member and transmitting rotation from the main body driving device. Engineering plastics such as polyamide, polyacetal, polyethylene terephthalate, polyphenylene sulfide, polyether ketone, liquid crystal polymer, polycarbonate, polyphenylene ether, polyarylate, polysulfone, polyethersulfone, polyetherimide, polyamideimide, etc. with excellent mechanical strength In order to control mechanical strength, rigidity, conductivity, etc., fibers such as glass fiber, carbon fiber, fillers such as carbon, talc, kaolin, calcium carbonate, alumina, silica, and various additives are used. Used by mixing. These flanges are press-fitted into a drum-like conductive support and fixed with an adhesive or the like.

[Examples 1 to 4 and Comparative Examples 1 to 8]
A subbing layer, a charge generation layer, a charge transport layer and a protective layer were applied in that order on an aluminum drum (conductive support) having a diameter of 30 mm, and then dried, and a plastic flange was press-fitted at both ends. A photoreceptor comprising a .5 .mu.m subbing layer, a 0.15 .mu.m charge generation layer, a 22 .mu.m charge transport layer, and a protective layer of about 4.5 .mu.m was prepared. Coating of the protective layer was performed by a spray method, and the others were performed by a dip coating method. 22.0% by mass of alumina having an average particle size of 0.21 μm was added to the protective layer. In this way, 120 photoconductors were produced. When the circumferential runout in the image forming area of the produced photoreceptor was measured, the average value was 35 μm, the minimum value was 5.1 μm, and the maximum value was 36 μm. Among the photoconductors prepared, those having a circumferential runout of 5.1 μm, 5.4 μm, 35 μm, 36 μm, and 112 μm were selected.

  On the other hand, as the charging roller, four types supplied from the charging roller manufacturer were used. These charging rollers are manufactured by attaching rubber-based materials in which carbon and an ion conductive material are mixed to a stainless steel cylinder, and the surface states of the charging rollers are different. The diameters of the four types of charging rollers were all 11.5 mm. A gap tape having a width of 10 mm and a thickness of 52 μm was attached to a position 13 mm from the end of each charging roller.

The surfaces of the four types of charging rollers were observed with an electron microscope, and the steps were measured using a three-dimensional SEM (ERA-8900FE; manufactured by ERIONIX) for all steps existing in 1 mm ² . In addition, the difference between the height differences of 2 μm and No. 4 existing in No. 1 to No. 4 was sampled and the difference of 400 μm or more was sampled. As a result, the No. 1 charging roller had no step of 2 μm or more. The No. 2 charging roller had 52 steps having a height of 2 μm or more continuous for 400 μm or more. When the step was sampled and linear approximation was performed using the least square method, the absolute value of the slope was 50 or more, and the correlation coefficient was 0.7 to 0.93. The No. 3 charging roller had 45 steps having a height of 2 μm or more continuous for 400 μm or more. When the step was sampled and linear approximation was performed using the least square method, the absolute value of the slope was 0.3 or less, and the correlation coefficient was 0.2 to 0.6. The No. 4 charging roller had 49 steps having a height of 2 μm or more that were continuous for 400 μm or more. When the step was sampled and linear approximation was performed using the least square method, the absolute value of the slope was 0.5 or less, and the correlation coefficient was 0.05 to 0.3.

  In the IPSIO CX400 (tandem type color image forming apparatus, manufactured by Ricoh), a charging roller is placed right above the photosensitive member, and the charging roller is pressed against the photosensitive member with a spring, and the linear velocity of the photosensitive member is 185 mm / second. Evaluation was performed by applying an AC voltage having a frequency of 1450 Hz and an amplitude of 1100 V superimposed on a DC voltage of −600 V between the photosensitive member and the charging roller.

  A No. 1 charging roller is incorporated into the black photoconductor unit, while photoconductors with circumferential runouts of 5.1 μm, 35 μm, and 112 μm are sequentially incorporated into the A4 size paper 1by1 halftone as shown in FIG. When five images were output and evaluated, a high-quality image was obtained with a photoreceptor with a circumferential shake of 5.1 μm, and a slight density unevenness was found with a photoreceptor with a circumference shake of 35 μm. A clear density unevenness was observed on the photosensitive member having a shake of 112 μm (comparative example 1 is a combination of a No. 1 charging roller and a 5.1 μm photosensitive member, and comparative example 2 is a combination of a No. 1 charging roller and a 35 μm photosensitive member) The combination of No. 1 charging roller and 112 μm photoconductor is Comparative Example 3).

  When the charging roller is changed to No. 2 charging roller and five 1by1 halftone images are output in the same manner, all the photoconductors with circumferential fluctuations of 5.1 μm, 35 μm, and 112 μm are fine in the vertical direction. Streaks were observed (combination of No. 2 charging roller and 5.1 μm photoreceptor in Comparative Example 4, Comparison of No. 2 charging roller and 35 μm photoreceptor in Comparative Example 5, No. 2 charging roller and 112 μm photoreceptor) The combination is Comparative Example 6). When the charging roller is changed to No. 3 charging roller and 1 by 1 halftone images are output five by five, a high-quality image is obtained on the photosensitive drums of 5.1 μm and 35 μm. A clear density unevenness was observed on the 112 μm photoconductor (the combination of the No. 3 charging roller and the 5.1 μm photoconductor is Example 1, the combination of the No.3 charging roller and the 35 μm photoconductor is the Example 2, No. .3 A combination of a charging roller and a 112 μm photoconductor is Comparative Example 7). When the charging roller is changed to No. 4 charging roller and 1 by 1 halftone images are output five by five, a high-quality image is obtained on a 5.1 μm or 35 μm circumferential runout, and the circumferential runout A clear density unevenness was observed on the 112 μm photoconductor (the combination of the No. 4 charging roller and the 5.1 μm photoconductor is Example 3, the combination of the No. 4 charging roller and the 35 μm photoconductor is the Example 4, No. A combination of .4 charging roller and 112 μm photoconductor is Comparative Example 8).

[Examples 5 to 7 and Comparative Example 9]
A charging roller and a photoconductor are incorporated in different combinations in each color photoconductor unit of the IPSIO CX400 (tandem type color image forming apparatus), and a total of 1500 1-by-1 halftone images are output for evaluation. After 70000 sheets were output continuously, the evaluation was performed again. No. 1 charging roller and 5.1 μm circumferential photoreceptor are incorporated in the black photosensitive unit, and No. 3 charging roller and 5.4 μm circumferential photoreceptor are incorporated in the cyan photosensitive unit. Built-in, No. 4 charging roller and circumferential photoreceptor 35 μm photoreceptor are incorporated into the magenta photoreceptor unit, and No. 4 charging roller and circumferential photoreceptor 36 μm photoreceptor are incorporated into the yellow photoreceptor unit. (The combination of No. 1 charging roller and 5.1 μm photoreceptor is Comparative Example 9, the combination of No. 3 charging roller and 5.4 μm photoreceptor is Example 5, and the combination of No. 4 charging roller and 35 μm photoreceptor is carried out. Example 6, a combination of No. 4 charging roller and 36 μm photoreceptor is Example 7).

  The black image developed from the black photoconductor unit in which the No. 1 charging roller and the photoconductor having a circumferential fluctuation of 5.1 μm were incorporated showed a slight density unevenness after output of 1500 sheets, and 70000 sheets. After the output, clear density unevenness was observed. With a cyan image developed from a cyan photoconductor unit incorporating a No. 3 charging roller and a photoconductor with a circumferential deflection of 5.4 μm, a high quality image is obtained after outputting 1500 sheets and after outputting 70000 sheets. It was. A magenta image developed from a magenta photoconductor unit incorporating a No. 4 charging roller and a photoconductor with a circumferential deflection of 35 .mu.m can be obtained after outputting 1500 sheets and after outputting 70000 sheets. A yellow image developed from a yellow photoconductor unit incorporating a No. 4 charging roller and a photoconductor having a circumferential runout of 36 μm can be obtained after outputting 1500 sheets and after outputting 70000 sheets. It was.

1 is a schematic configuration diagram of an image forming apparatus according to the present invention. It is a figure explaining the micro gap of a charging roller and a photoreceptor. 3 is an electron micrograph of a charging roller surface. It is the figure which extracted the typical level | step difference line from the photograph of FIG. 3 to XY plane. It is a graph explaining the case where it samples about a level | step difference and performs a linear approximation by the least squares method. It is explanatory drawing of the hybrid image at the time of performing image evaluation. It is a figure explaining the 1st speed fixed example regarding circumferential runout.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 4 Static elimination lamp 5 Charging apparatus 6 Laser writing unit 7 Developing apparatus 8 Transfer apparatus 9 Fixing apparatus 12 Cleaning apparatus

Claims (6)

In an image forming apparatus that performs an electrification process by applying an AC voltage superimposed with a DC voltage to an image carrier and a charging roller arranged in non-contact with the image carrier.
The circumferential runout in the image forming area of the image carrier is 4 to 100 μm,
The charging roller has a plurality of steps on the surface thereof that have a height difference of 2 to 30 μm and a length of 400 μm or more.
Using the longitudinal center axis of the charging roller as the X axis, the plurality of steps are extracted on the XY plane and plotted, and when the steps are linearly approximated by the least square method, the correlation coefficient is 0.9 or less and the slope is An image forming apparatus having a value of 0.5 to 0.5.   2. The image forming apparatus according to claim 1, wherein the gap between the image forming area of the charging roller and the image carrier is 10 to 150 [mu] m on average when the image carrier and the charging roller are stationary. 85% of the step in the area of 0.36 to ⁴ mm ^{2 at} one end or both ends of the center of the peripheral surface of the charging roller and the image forming area has a height difference of 2 to 30 μm and a length of 400 μm or more. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   3. The image forming apparatus according to claim 1, wherein the number of times of sampling when extracting and plotting the plurality of steps on the XY plane is 10 or more. 4.   The image forming apparatus according to claim 1, wherein a maximum resolution capable of forming an image is 1000 dpi or more.   A process cartridge comprising at least a charging roller and an image carrier that can be mounted on the image forming apparatus according to claim 1.