JP2007121334A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus wherein uniform charging potential is obtained by efficiently charging a photoreceptor, and also, the speed of the oxidation deterioration in the photoreceptor and a charging roller is reduced, then, the lives of the photoreceptor and the charging roller are prolonged. <P>SOLUTION: In the image forming apparatus, when the photoreceptor 1 is charged for a fixed time with an alternate frequency (fs) as a design value while stopping the photoreceptor 1, C-C coupling contained in the organic substance on the surface of the photoreceptor is separated, and discharge marks arise. When fO=v/wO is established, provided that the mean value of the width of the discharge mark is expressed by wO and the photoreceptor linear speed at the image formation is expressed by v, by setting AC frequency (f) at the image formation within an extent of ≥2.2 times and ≤13 times as much as (fo) instead of the design value fs, the frequency of replacing the photoreceptor and the charging roller is reduced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a charging roller in an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof.

  In an image forming apparatus using an electrophotographic process, an image is formed by charging a photosensitive member, exposing, developing, transferring, and fixing. In the charging process, a scorotron charger has been conventionally used. However, due to environmental problems, a charging roller that generates less harmful gases such as ozone and NOx and can reduce the size of the device is used as the charger. When image formation is performed in a state where the charging roller is in contact with the photosensitive member, the residual toner after transfer may not be completely cleaned, and the residual toner adheres to the charging roller, resulting in variations in the resistance of the charging roller. As a result, the charged potential of the photoconductor varies, causing image density unevenness. Therefore, a method has been proposed in which a gap is provided between the photosensitive member and the charging roller to charge the photosensitive member (see, for example, Patent Document 1). In this charging step, the charging potential of the photosensitive member can be set to the target voltage by applying an AC voltage to the target member and an AC voltage. The charging parameters at this time include the AC voltage and frequency to be applied, uneven resistance of the charging roller, uneven resistance of the photosensitive member, the size of the gap between the photosensitive member and the charging roller, and variations in the gap. There is a proposal of a control means for detecting an occurrence of variation in the gap and determining an applied voltage corresponding to the gap (see, for example, Patent Document 2). In addition, there is a proposal of a technique for charging the surface of the image carrier to a predetermined constant value even if the gap varies or fluctuates (see, for example, Patent Document 3).

  The applied AC voltage determines the distance between the photosensitive member and the charging roller that can cause discharge, and the larger the applied AC voltage, the more the discharge can occur even when the distance between the photosensitive member and the charging roller increases. . For this reason, as the alternating voltage to be applied increases, discharge occurs in a wider area of the charging roller, so that the charging unevenness of the photoreceptor can be reduced. However, since discharging is a process in which charged particles such as ions and electrons are exposed to the photosensitive member and the charging roller, oxidation deterioration of the photosensitive member and the charging roller occurs. When the AC voltage to be applied is large, the amount of charged particles generated and their energy increase particularly when the distance between the photoconductor and the charging roller is small, so that the oxidative deterioration of the photoconductor and the charging roller becomes severe. In addition, the charging roller must be replaced early. The applied AC frequency determines the number of times that discharge can occur per unit time. Therefore, the larger the applied AC frequency, the smaller the charging unevenness of the photoconductor. When the frequency is high, the photoconductor and the charging roller undergo oxidative deterioration, and the photoconductor and the charging roller must be replaced early.

  Further, if the distance between the photosensitive member and the charging roller is too close, no discharge will occur, and according to Paschen's law, no discharge will occur at about 7 μm or less. However, in reality, due to the electric capacity of the photoconductor and the resistance of the charging roller, it is said that the distance between the photoconductor and the charging roller where discharge begins to occur is approximately 20 μm or more. For this reason, it is very important to control the distance between the photosensitive member and the charging roller in units of μm. However, in reality, the charging roller has a surface roughness of μm unit, so that the charging unevenness of the photosensitive member is reduced. In many cases, the value of the applied AC voltage and frequency is set to be high so as to eliminate the above. As for the discharge between the photosensitive member and the charging roller, the electric field strength is high when the distance between the photosensitive member and the charging roller where discharge begins to occur is approximately 20 μm. It will be intense. Therefore, if the distance between the photoconductor and the charging roller is sufficiently large, the oxidative deterioration of the photoconductor and the charging roller can be suppressed. However, if the distance is too large, the discharge will vary, and conversely, the AC If the voltage and frequency are low, the charged potential of the photoreceptor will not be uniform, resulting in an abnormal image. Usually, since image quality is often given priority, the applied AC voltage and frequency inevitably tend to be set higher.

Therefore, the image forming apparatus is often determined in a state where vibration prevention and assembly accuracy are not perfect. Therefore, in order to make the charging potential of the photosensitive member uniform, the AC voltage and frequency applied to the charging roller have a large value. This is often set, and the oxidative deterioration of the photoreceptor and the charging roller is accelerated. It is sufficient if the life of the photoconductor and the charging roller is set to be low and the photoconductor and the charging roller are replaced in a short cycle. However, in order to reduce maintenance costs and replacement costs, make the charging conditions as gentle as possible. Must be set.
However, in Patent Document 2 and Patent Document 3, as described above, it is difficult to accurately see how charging (discharging) occurs. Therefore, it is only necessary to measure the charging potential of the photosensitive member. It was not possible to estimate the quality. In addition, the measurement of the charging potential of the photoconductor can usually be performed only by the average of the charging potential in an area of about 1 cm in diameter, and the local charging potential that is affected when writing at high resolution is performed. It was not possible to detect the variation of. In addition, the measurement of the charging potential of the photosensitive member is currently performed only at a few limited places. Therefore, the charging condition may be set higher so that the charging potential tends to be constant. In many cases, the life of photoconductors and charging rollers has been shortened.
In addition, if the surface of the photoconductor or charging roller is oxidized and deteriorated, the toner component easily adheres to the photoconductor or charging roller, and the adhering material is oxidized by discharge and becomes ionic. This is likely to occur, and blur is likely to occur on the photoconductor and streaky abnormal images on the charging roller. Therefore, relaxing the charging condition is important for suppressing these abnormal images.

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

  The present invention provides an image forming apparatus that obtains a uniform charging potential by performing efficient charging, reduces the rate of oxidative deterioration of the photosensitive member and the charging roller, and has a long life of the photosensitive member and the charging roller. Is.

In the first aspect of the present invention, a photoconductor, a charging roller that is not in contact with the photoconductor, a power source that charges the surface of the photoconductor by applying an AC voltage in which a DC voltage is superimposed on the charging roller, In the image forming apparatus, the voltage from the power source is applied to the charging roller for a certain period of time without rotating at least the photoconductor, and the discharge mark in the image forming area generated on the photoconductor is the length of the photoconductor. The width of the two discharge marks obtained by setting the distance between the photosensitive member and the charging roller, the voltage value of the DC voltage, and the voltage value of the AC voltage so as to form two stripes continuous in the direction. Is the frequency f (Hz) at the time of image formation of the AC voltage, where w0 (mm) is the average speed of the photoconductor and v (mm / sec) is the linear velocity at the time of image formation, and f0 = v / w0. ) Over 2.2 times f0, 13 Characterized by the following.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, when the width of the gap between the two stripes is ws (mm), ws is 1% or more of 2 × w0, It is characterized by being 33% or less.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the predetermined time is set to (fs / 1000 to fs / 10), where fs is a design alternating frequency. Features.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, a linear velocity at the time of image formation of the photoconductor is v ≧ 150.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the outer diameter of the charging roller is 9 mm or more and 25 mm or less.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the image forming apparatus is of a tandem type.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the maximum resolution of an image that can be formed is 1000 dpi or more. .

According to the present invention,
In the image forming apparatus using the non-contact charging roller, by determining the frequency f of the alternating voltage superimposed on the direct current voltage based on at least two discharge marks generated when charging without rotating the photosensitive member, It is possible to provide an image forming apparatus capable of forming a high-quality image and requiring less frequent replacement of the photoreceptor and the charging roller.
By determining the range of the width of the gap between the two discharge marks, it is possible to set the image forming conditions so that the frequency of replacement of the photoconductor and the charging roller is reduced.
Alternatively, by defining the range of the design value fs of the AC frequency, it is possible to set the image forming conditions so that the replacement frequency of the photosensitive member and the charging roller is reduced.
By defining the linear velocity of the photoconductor during image formation and the outer diameter range of the charging roller, high-quality image formation is possible while making the charging process compact, and the image that requires less replacement of the photoconductor and the charging roller. A forming apparatus can be provided.

Until now, there has been no simple method for accurately determining whether the charging process is operating well. As a result of various studies, in the charging process in which the photosensitive member is charged by applying an alternating voltage on which a direct current voltage is superimposed on a charging roller arranged in a non-contact manner with the photosensitive member, the photosensitive member is partially discharged by a discharge. It has been noted that the energy is so high that the C—C bond of the organic substance of the charging roller and the photoreceptor is broken. Therefore, if an AC voltage superimposed with a DC voltage is applied for a long time without rotating at least the photosensitive member and the charging roller, the charged roller (when not rotated) and the photosensitive A streak-like defect (called a discharge trace) is found in the body, and the stripe-like discharge trace is caused by variations in the distance between the photoconductor and the charging roller and variations in the electrical characteristics of each. It has been found that the unevenness of the generated discharge can be visualized.
As a result of investigating whether or not the discharge can occur in a uniform charge potential to the photoconductor while suppressing the rate of oxidative degradation of the photoconductor and the charge roller with gentle charging, As long as the discharge distance between the body and the discharge limit distance is longer, the smaller the gap between the charging roller and the photosensitive body, the lower the energy and the more efficient it can be, and the generation of oxidizing gases such as ozone and NOx is also possible. It was found that it can be kept low.

  However, if the charging roller and the photoconductor are too close, the toner that could not be cleaned will be caught between the charging roller and the photoconductor, causing streaky abnormal images, and the gap between the photoconductor and the charging roller will be about 20 μm or less. In this case, a portion where discharge does not occur occurs, and a portion where discharge occurs occurs. When the region where the discharge does not occur becomes wide, the charging potential unevenness must be increased unless the frequency of the AC voltage applied to the charging roller is increased. It was found that it cannot be solved. If the width of the place where the discharge does not occur is narrower than the width of the place where the discharge occurs, the charging potential of the photoreceptor can be made uniform even under mild charging conditions. The present inventors have found that the speed of oxidation degradation can be significantly reduced. That is, the present invention includes at least a photoconductor, a charging roller that is not in contact with the photoconductor, and a power source that charges the surface of the photoconductor by applying an AC voltage in which a DC voltage is superimposed on the charging roller. In the image forming apparatus, the voltage from the power source is applied to the charging roller for a certain period of time without rotating the photosensitive member, and two stripes in which discharge traces in the image forming area generated on the photosensitive member are continuous. The average value of the widths of the two discharge marks obtained by setting the distance between the photosensitive member and the charging roller, the voltage value of the DC voltage, and the voltage value of the AC voltage is w0 (mm). When the linear velocity at the time of image formation of the photoconductor is v (mm / second) and f0 = v / w0, the frequency f (Hz) at the time of image formation of the AC voltage is 4.5 × f0 or more, 26 × f0 or less The image forming apparatus.

In the determination of the AC frequency according to the present invention, for example, in the manufacturing stage of an image forming apparatus, discharge is performed at the expense of the photosensitive member for one or several units with respect to an apparatus that should be made according to the design value. A mark is generated and used to determine the final f from the observation result. It is possible that the determined f is different from the design value fs. If f is determined, for the product to be shipped, the AC frequency is set by adjusting the variable part using the value. The same processing should be performed even when the lot of parts having a large influence on the charging characteristics, such as a photoconductor and a charging roller, is changed. A photoconductor with a charging mark cannot be used in an image forming apparatus. However, a plurality of data can be obtained by rotating the photoconductor a little and repeating the generation of the charging traces on the new surface in the same procedure as described above. Even when the charging roller is used without being rotated, a discharge mark is generated on the charging roller, but a plurality of data can be taken as described above.
In the image forming apparatus according to the present invention, an AC voltage superimposed with the DC voltage is applied for a certain period of time without rotating the photoconductor, and a method for obtaining discharge traces in the image forming area generated on the photoconductor is as follows. Either a forming apparatus or a unit consisting only of a photosensitive member and a charging roller may be used, but the voltage applied to the charging roller and the photosensitive member must be that used in an actual image forming apparatus. Normally, in an actual image forming apparatus, the electric current flowing in the charging process is controlled in consideration of the electric characteristics of the charging roller and the photosensitive member due to environmental fluctuations, and the AC voltage applied to the charging roller is changed. There are many.
In this case, the application conditions are preferably set in an environment where the image forming apparatus is mainly used (for example, a temperature of 23 ° C. and a humidity of 55%).

  Usually, the voltage applied to the charging roller is a DC voltage of 300 to 900 (-V), preferably 400 to 800 (-V), and more preferably 450 to 700 (-V). A DC voltage applied to the charging roller of 300 (−V) or less is not preferable because the charging potential of the photoconductor is low, a sufficient light attenuation curve of the photoconductor cannot be obtained, and it is difficult to form a high-quality image. . When the voltage applied to the charging roller is 900 (-V) or more, when the film thickness of the photosensitive member becomes thin, the carrier in the developer adheres to the photosensitive member and generates an abnormal image of a spot or the background is stained. This is not preferable because an abnormal image is easily generated. The AC voltage applied to the charging roller is 1500 V to 3000 V, preferably 1600 V to 2700 V, more preferably 1700 V to 2500 V as a peak-to-peak. When the AC voltage applied to the charging roller is 1500 V or less, the charging potential unevenness of the photoconductor is likely to occur. Is undesirably shortened because the life of the photosensitive member and the charging roller is shortened. The frequency of the AC voltage applied to the charging roller is appropriately determined depending on the linear velocity of the photosensitive member and the resolution of the image to be formed, but is 300 Hz to 4000 Hz, preferably 500 Hz to 3000 Hz, more preferably 600 Hz to 2500 Hz. It is. If the frequency of the AC voltage applied to the charging roller is 300 Hz or less, the charging unevenness of the photosensitive member is likely to occur, and an abnormal image of horizontal stripes is likely to occur, which is not preferable. When the frequency of the AC voltage applied to the charging roller is 4000 Hz or more, the speed of oxidation deterioration of the photosensitive member and the charging roller becomes extremely fast, and the life of the photosensitive member and the charging roller is shortened.

  In the image forming apparatus of the present invention, in order to observe the discharge trace generated on the photosensitive member, the time for applying the voltage to the charging roller may be any voltage as long as the discharge trace can be observed. Since it appears earlier as the frequency fs (Hz) in alternating current design increases, it is preferable to set it to (fs / 1000 to fs / 10). For example, when the frequency is 2000 Hz, the application time is preferably 2 to 20 minutes. Preferably it is (fs / 500 to fs / 20) minutes, more preferably (fs / 250 to fs / 25) minutes. If the applied time is less than (fs / 1000) minutes, the discharge traces are unclear, so it is difficult to accurately determine the width of the discharge traces. If longer than (fs / 10) minutes, the photoreceptor and the charging roller are damaged. In particular, in the case of a photoreceptor or charging roller having a surface layer, when the surface layer disappears due to charging, the rate of oxidative deterioration below the surface layer is often increased, which is not preferable because it is dangerous.

FIG. 1 is a schematic diagram for explaining discharge traces generated on a photoreceptor.
In the figure, reference numerals w1 and w2 denote the width of the discharge trace, and ws denotes a gap between the two discharge traces.
In the image forming apparatus of the present invention, discharge traces generated on the photosensitive member are schematically shown in FIG. The discharge trace can be observed with an optical microscope, an electron microscope or the like at a magnification of about 5 to 50 times.
In the image forming apparatus of the present invention, various conditions such as the gap of the discharge region and the voltage value are set so that the discharge trace generated on the photoconductor extends long in the longitudinal direction of the photoconductor and substantially two are generated. That is, a region where no discharge occurs (no discharge region) exists between the two discharge marks. Although referred to as a non-discharge region, there may be an island-like region where discharge occurs due to slight unevenness of the charging roller or the photoreceptor. Each of the two discharge traces is a region where the photoreceptor is continuously deteriorated.
Of course, the conditions can be set so that there is only one discharge mark. As described above, if the gap is sufficiently large, no discharge region is generated. In this case, it is not known whether the gap is the minimum necessary. In the present invention, the reason why the non-discharge region is intentionally generated is to make the distance between the photosensitive member and the charging roller as close as possible so that the gap is minimized. Therefore, it is preferable to set the non-discharge area to be as small as possible as long as it can be recognized.

In the image forming apparatus of the present invention, the discharge traces generated on the photosensitive member are two streaks as described above. If the apparatus is configured as designed, in principle, the widths of the two discharge marks are equal. In the case of measured data, the widths may not be equal due to various manufacturing errors, assembly errors, etc., but the difference is usually negligible. In the following description, the widths of the two stripes are treated as being equal to each other, but in order to include the case where they are not equal, the average value w0 of both is used as necessary. That is, w0 = (w1 + w2) / 2.
The total width w1 + w2 = 2 × w0 (mm) of the two stripes is 0.7 mm or more, preferably 0.8 to 2.0 mm, and more preferably 0.9 to 1.8 mm. If w0 is 0.7 mm or less, the dischargeable region is too narrow and charging unevenness is likely to occur. For this reason, the frequency of the alternating current applied to the charging roller must be set high, and the deterioration rate of the photosensitive member is increased. Absent. A larger w0 is preferable because a uniform charging potential is easily obtained. If the diameter of at least one of the photosensitive member and the charging roller is increased, a region where the distance between the photosensitive member and the charging roller that can generate discharge is within a certain range is defined. Since it becomes wider, w0 can be increased. However, if the diameter of at least one of the charging roller and the photosensitive member is too large, the apparatus becomes large, and unless the accuracy of assembly is increased, the width in which discharge occurs easily varies depending on the location, and the variation in the width of the discharge mark is large. turn into. Therefore, the outer diameter of the charging roller is suitably 9 to 25 mm, preferably 10 to 20 mm.

In the image forming apparatus of the present invention, since discharge is generated in each of the two stripes of the discharge trace generated on the photosensitive member, the total width of the two stripes is important, and the width of each stripe is not necessarily limited. It doesn't have to be the same. However, in principle, the widths of the two lines should be the same, so if the widths of the two lines are different, there are often problems with the shape of the photoconductor or charging roller and the assembly accuracy. The widths are preferably equal.
In the image forming apparatus of the present invention, when w is the total width of the charged region that can be measured from the discharge trace generated on the photoreceptor,
w = w1 + w2 + ws = 2 × w0 + ws
It becomes.
The gap between the two stripes, that is, the width (wsmm) of the non-discharge region is 1% or more and 33% or less of w, preferably 3 to 20%, more preferably 5 to 10%. If ws exceeds 33% of w, charging potential unevenness tends to occur, which is not preferable. If it is less than 1%, it is difficult to measure the width ws of the non-discharge region, and if the AC voltage required for charging is not increased, uneven charging tends to occur, and the life of the photoreceptor and the charging roller is shortened, which is not preferable.

FIG. 2 is a conceptual diagram showing a charged state by a uniform charge distribution on the photoreceptor surface.
FIG. 3 is a conceptual diagram showing a charged state due to non-uniform charge distribution.
In both figures, reference numerals 1 to 12 denote virtual blocks in which the surface of the photoconductor is divided into AC half-cycle units for convenience, p is a fixed position with respect to the photoconductor moving surface, t is time, T is an AC cycle, and Vs is a charging potential. Respectively.
To make the charging potential uniform, it is effective to set the frequency of the AC voltage applied to the charging roller to a high value. However, if the frequency is set too high, the speed of oxidative deterioration of the photoconductor and the charging roller will be increased. This is not preferable because the photosensitive member and the charging roller must be replaced early.
In the image forming apparatus of the present invention, it is possible to specify the place where the discharge is generated by the discharge trace, so that the frequency of the alternating current applied to the charging potential can be set to an appropriate value, and the photosensitive member and the charging It is possible to greatly increase the interval for exchanging the rollers.
In the image forming apparatus of the present invention, when the linear velocity of the photosensitive member is v (mm / second), ideally f ≧ v / w0.
If this is the case, the charged potential of the photoreceptor is constant. Ideal is the case where it is assumed that the discharge areas of w1 and w2 are uniformly charged by the discharge in one cycle of alternating current. Actually, reverse discharge also occurs, but it is assumed here that reverse discharge does not occur.

Both figures show an AC waveform and a charged state due to movement of the photoreceptor surface when f = v / w0. The vertical direction represents a change in time, and the horizontal direction represents a change in position due to the movement of the photosensitive member. In order to simplify the explanation, the case of w1 = w2 = ws was taken as an example. Therefore, ws is approximately 33% of w = w1 + w2 + ws.
The actual charging is negative charging, but the charging potential is displayed upward for easy understanding. In addition, since the AC potential is also superimposed on the DC potential, the side where the absolute value of the potential is increased is indicated by +.
Considering as a model, charging is performed at the moment when the time when the AC potential reaches the maximum value on the + side in the figure is slightly exceeded. Here, for the sake of convenience, the charging potential at which the photosensitive member is charged in the section is shown at the position where the potential becomes maximum in the time zone. The charged potential of each block of the photoconductor denoted by reference numerals 1 to 12 is indicated at the position of each discharge area as to the magnitude charged until it leaves the discharge area. Actually, since the photosensitive member is charged while moving, the area of the photosensitive member that is charged from one charged area during the half cycle of the alternating current is equivalent to two blocks. This will be described in detail with reference to the drawings.
When the discharge is started at time t0, the photoconductor surface located at the initial position p0 advances to the position p1 during an AC half cycle (T / 2). Similarly, the photoreceptor surface at the initial position p1 proceeds to the position p2, and the photoreceptor surface at p2 proceeds to p3. Accordingly, during this time, the region that has existed even once in the charging region 1 is two blocks from the position p0 to the position p2.
However, the time that exists in the charged region differs depending on the location, and the time decreases as it goes to the end of the two blocks. Therefore, the display is simplified on the assumption that charging is concentrated in one block including the center.
FIG. 2 shows an example in which each block that passes through the charging area is uniformly charged in the entire block. In contrast, FIG. 3 shows an example in which the charge distribution in the block has a mountain shape and the maximum value is somewhere other than both ends. Although the figure shows the case where the peak is substantially at the center, in the actual measurement of the depth of the discharge trace, it is estimated that each peak position is closer to the side where the gap exists.

When f = v / w0, an arbitrary point on the surface of the photoreceptor is in a relationship of being charged only once from one charged region. Accordingly, all points on the photoreceptor surface pass through the charged region twice.
In the case of the uniform charging shown in FIG. 2, it can be seen that the surface of the photosensitive member that has passed through the two charged regions is uniformly charged. When the same block is charged twice, the charging potential is not a simple addition, but is shown in a simplified manner.
In the case of the non-uniform charging shown in FIG. 3, since the charging potential of the block that has passed through each charging area is non-uniform, the block that has passed through the two charging areas also becomes non-uniform charging. As one method for solving this problem, as can be inferred from the same figure, a method of reducing the width ws of the gap to half of w0 is conceivable. That is, when ws is set in this manner, the boundary portion of each block charged in the charging region 1 is charged at the central portion of the next charging region 2, so that the both ends and the center of each block are charged substantially the same. Level and close to uniform charging. However, in this case, it is expected that the charging unevenness is considerably increased.
As another means for solving the above problem, there is a method of increasing the AC frequency. That is, a certain point on the photosensitive member surface is charged not only once but a plurality of times while passing through the charging region.

As described above, in the discharge of one cycle of the AC voltage applied to the charging roller, there is a nonuniform distribution in the charging potential that the end is lower in the range of the width of the discharge mark, so the frequency is higher. It needs to be bigger. As a result of the experiment, it was found that f0 = v / w0 should be replaced and the range of 13 × f0 ≧ f ≧ 2.2 × f0 should be set. Preferably 11 × f0 ≧ f ≧ 2.5 × f0, more preferably 10 × f0 ≧ f ≧ 2.7 × f0.
If the frequency is smaller than 2.2 × f0, the uniformity of the charged potential of the photoreceptor cannot be obtained, and is particularly necessary for obtaining a high-quality image in an image forming apparatus having a resolution of 1000 dpi, preferably 1200 dpi or more. It is difficult to ensure a charging unevenness of 30 V or less, preferably 20 V or less, more preferably 10 V or less, and a high quality image cannot be obtained. If the frequency is higher than 13 × f0, the speed of oxidation deterioration of the photosensitive member and the charging roller is high, and it is not preferable because the photosensitive member and the charging roller must be replaced at an early stage.

  The image forming apparatus of the present invention can provide an image forming apparatus with high image quality and high reliability regardless of the linear speed of the photosensitive member, but the linear speed is preferably 150 mm / second or more. Is 220 mm / second or more, more preferably 280 mm / second to 800 mm / second, the speed of oxidative degradation of the photosensitive member and the charging roller can be slowed down, and the life of the photosensitive member and the charging roller can be extended. Therefore, it is preferable. This is because the image forming apparatus of the present invention performs efficient charging. In the conventional charging process, the place where the discharge occurs strongly and the place where the discharge occurs weakly coexist. Therefore, in order to make the charged potential of the photosensitive member uniform, the place where the discharge occurs weakly, The charging conditions were determined. Even in the conventional charging process, when the linear velocity of the photosensitive member is low, the influence is not so great. However, as the linear velocity of the photosensitive member increases, the variation in the charging potential of the photosensitive member increases, so the charging conditions are strengthened. As a result, the speed of oxidation deterioration of the photosensitive member and the charging roller is increased, and the photosensitive member and the charging roller have to be replaced at an early stage.

In the photoreceptor used in the image forming apparatus of 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 provided on the charge transport layer. There is a reverse layer type. 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. In addition, an appropriate amount of a plasticizer, an antioxidant, a leveling agent and the like can be added to each layer as necessary.
Examples of the conductive support for the photoreceptor include those having a volume resistance of 10 ¹⁰ Ω · cm or less, for example, metals such as aluminum, nickel, chromium, nichrome, copper, gold, silver, platinum, tin oxide, oxidation A metal oxide such as indium is deposited or sputtered to form a film or cylindrical plastic, paper coated, or a plate of aluminum, aluminum alloy, nickel, stainless steel, etc. After forming the tube into a drum shape, it is possible to use a tube that has been surface-treated by cutting, superfinishing, polishing, or the like. A drum-shaped support 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 20 mm or less, it is physically difficult to arrange the charging, exposure, development, transfer, and cleaning steps around the drum. If the diameter of the drum-shaped support is 150 mm or more, image formation is performed. The apparatus becomes undesirably large. 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. Endless nickel belts and endless stainless steel belts can also be used as the conductive support.

  As the undercoat layer of the photoreceptor used in the image forming apparatus of the present invention, a resin, or a material mainly composed of a white pigment and a resin, a metal oxide film obtained by chemically or electrochemically oxidizing the surface of a conductive substrate, etc. However, those containing a white pigment and a resin as main components are preferable. Examples of the white pigment 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 the conductive substrate. As the resin used for the undercoat layer, thermoplastic resins such as polyamide, polyvinyl alcohol, casein, and methyl cellulose, thermosetting resins such as acrylic, phenol, melamine, alkyd, unsaturated polyester, and epoxy, one or various kinds of these Mixtures can be exemplified.

  Examples of the charge generating material for the photoreceptor used in the image forming apparatus of the present invention include azo pigments such as monoazo pigments, bisazo pigments, trisazo pigments, and tetrakisazo pigments, triarylmethane dyes, thiazine dyes, and oxazines. Dyes, xanthene dyes, cyanine dyes, styryl dyes, pyrylium dyes, quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, bisbenzimidazole pigments, indanthrone pigments, squarylium pigments Inorganic materials such as pigments, organic pigments and dyes such as phthalocyanine pigments, selenium, selenium-arsenic, selenium-tellurium, cadmium sulfide, zinc oxide, titanium oxide, and amorphous silicon can be used. It can be used alone or in combination.

  Examples of the charge transport material for the photoreceptor used in the image forming apparatus of the present invention include anthracene derivatives, pyrene derivatives, carbazole derivatives, tetrazole derivatives, metallocene derivatives, phenothiazine derivatives, pyrazoline compounds, hydrazone compounds, styryl compounds, styryl hydrazone compounds, Enamine compounds, butadiene compounds, distyryl compounds, oxazole compounds, oxadiazole compounds, thiazole compounds, imidazole compounds, triphenylamine derivatives, phenylenediamine derivatives, aminostilbene derivatives, triphenylmethane derivatives, etc. can do.

  The binder resin used to form 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 resin Examples include silicone resins, thermosetting resins such as thermosetting acrylic resins, one kind of binder resins such as photoconductive resins such as polyvinyl carbazole, polyvinyl anthracene, and polyvinyl pyrene, and a mixture of various kinds of binder resins. In particular, it is not limited to these.

As antioxidant, the following are used, for example.
Monophenol compounds 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 and the like.
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) and the like.
High molecular 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 and the like.

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, and the like.
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 and the like.

Organic sulfur compounds Dilauryl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, ditetradecyl-3,3′-thiodipropionate, and the like.
Organic phosphorus compounds such as 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 in the charge transport layer. As the leveling agent, silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, polymers or oligomers having a perfluoroalkyl group in the side chain are used, and the amount used is 100 parts by weight of the binder resin. 0 to 1 part by weight is suitable.

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 for the protective layer, ABS resin, ACS resin, olefin-vinyl monomer copolymer, chlorinated polyether, allyl resin, phenol resin, polyacetal, polyamide, polyamideimide, polyacrylate, polyallylsulfone, polybutylene, poly Butylene terephthalate, polycarbonate, polyethersulfone, polyethylene, polyethylene terephthalate, polyimide, acrylic resin, polymethylbenten, polypropylene, polyphenylene oxide, polysulfone, polystyrene, AS resin, butadiene-styrene copolymer, polyurethane, polyvinyl chloride, polychlorinated Examples thereof include resins such as vinylidene and epoxy resins. Examples of the metal oxide include aluminum oxide, 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 inorganic materials such as aluminum oxide, titanium oxide, zinc oxide, and indium oxide are dispersed in these resins for the purpose of improving wear resistance. Things can be added. 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.
As a solvent used for producing the photoreceptor, a chlorine-based solvent such as dichloromethane, tetrahydrofuran, dioxane, toluene, cyclohexanone, methyl ethyl ketone, acetone and the like are used.

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

In the image forming apparatus of the present invention, high-quality image formation is possible in both monochrome image formation and color image formation, but it is particularly effective in color image formation that requires high-quality image formation. The life of the photosensitive member and the charging roller can be greatly extended while forming the image. When the image forming apparatus of the present invention can form a color image, a single photoconductor is used. After developing each color toner on the photoconductor, the intermediate transfer body or the image carrier is sequentially formed on the photoconductor of each color. The image is formed by transferring the toner image of the toner, the 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 to form an image. Both of the tandem type image forming apparatuses to be performed have excellent performance. In the tandem image forming apparatus, in order to suppress generation of oxidizing gas such as ozone accompanying charging, it is necessary to take a charging process by a charging roller. The charging process used in the image forming apparatus of the present invention has a charging condition. Since it is gentle, the amount of oxidizing gas generated is particularly small. Therefore, the image forming apparatus of the present invention is an excellent image forming apparatus that is not only capable of high-quality and high-reliability image formation but also is environmentally friendly.
The charging method evaluation method of the present invention will be described in more detail with reference to the drawings.

FIG. 4 is a conceptual diagram showing an image forming apparatus to which the present invention is applied.
In the figure, reference numeral 1 is a photosensitive member, 2 is a conductive base, 3 is a photosensitive layer, 4 is a static elimination lamp, 5 is a charging device, 6 is a laser writing unit, 7 is a developing device, 8 is a transfer device, and 9 is a fixing device. Reference numeral 10 denotes a fixing roller, 11 denotes a pressure roller, 12 denotes a cleaning device, 13 denotes a charging roller, 14 denotes a power source, G denotes a minute gap, L denotes an exposure light beam, and P denotes a transfer material.
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. In a main body housing (not shown), a photosensitive member 1 as an example of a member to be charged is disposed. This photosensitive member 1 is a photosensitive member in which a photosensitive layer 3 is laminated on the outer peripheral surface of a conductive base 2 on a drum. Consists of. It is also possible to use a photoreceptor composed of a belt-shaped photoreceptor that is wound around a plurality of rollers and driven, or a drum-shaped or belt-shaped photoreceptor composed of a dielectric.
During the image forming operation, the photosensitive member 1 is rotated in the clockwise direction in the figure, and the surface thereof moves in the direction of arrow A. At this time, the surface of the photoconductor is irradiated with light from the charge eliminating lamp 4, the surface is initialized, and then the photoconductor surface 3 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 L 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 made of transfer paper, for example, is fed between the transfer device 8 and the photoconductor 1 facing the photoconductor 1 at a predetermined timing. At this time, a toner image formed on the photoconductor Is electrostatically transferred onto the transfer material P. The transfer material P onto which the toner image has been transferred continues to pass between the fixing roller 10 and the pressure roller 11 of the fixing device 9, and at this time, the toner image is fixed on the transfer material by the action of heat and pressure. 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 has a charging roller 13 disposed opposite to the surface of the moving object to be charged, in the illustrated example, the surface of the photosensitive member 1, and a power source 14 for applying 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 photosensitive member surface 3 to charge the photosensitive member surface 3 to a predetermined polarity.
The layer structure of the charging roller 13 is preferably composed of a polymer layer and a surface layer on a conductive support.
The conductive base (support) 2 functions as an electrode and a support member of the charging roll. For example, a metal or alloy such as aluminum, copper alloy, stainless steel, iron that has been plated with chromium, nickel, or the like, It is made of a conductive material such as a conductive agent resin.

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 roll used in the image forming apparatus of the present invention, polyester-based, olefin-based thermoplastic elastomer, polystyrene, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene- Styrenic thermoplastic resins such as acrylonitrile copolymer, isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, urethane rubber, silicone rubber, fluorine 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 Emissions copolymer rubber, natural rubber, and blends the rubber material. 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 fine powders such as various conductive metal oxides such as tin oxide-antimony oxide solid solution and tin oxide-indium oxide solid solution; 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 ultrafine hardness of the surface of the charging roller 13 is 0.04 or more and 0.5 or less, as described above. Vinylidene, 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, ethylene vinyl acetate copolymer and the like.
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 1,000 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 charging roller 13 shown in the figure is opposed to the surface of the photoreceptor with a small gap G of, for example, 8 to 50 μm, preferably 10 to 45 μm, and more preferably 10 to 40 μm. When the minute gap G is 8 μm or less, the toner additive and the small particle size toner that could not be cleaned in the cleaning process are easily caught on the charging roller, and the resistance of the charging roller at the caught portion becomes high, resulting in a streak image. This is not preferable because it tends to occur. When the minute gap G is larger than 50 μm, it is necessary to increase the AC voltage applied to the charging roller, which is not preferable because the speed of oxidation deterioration of the photosensitive member and the charging roller is increased.

FIG. 5 is a diagram showing a configuration example for forming a minute gap between the charging roller and the surface of the photosensitive member.
In the figure, reference numeral 20 denotes a spacer, and G denotes a gap.
A tape is affixed to the charging roller 13 as spacers 20 at both end regions in the longitudinal direction. The tape used is a base polymer in which an adhesive is laminated on polyester, polyimide, or fluororesin. When these tapes come into contact with the surface of the photoconductor, the charging roller 13 maintains a minute gap G with respect to the surface of the photoconductor. Further, the minute gap G can be secured by using a flange or the like instead of the tape.
In the image forming apparatus of the present invention, it is very preferable that the photosensitive member, the charging roller, the developing and cleaning device are integrated into a so-called process cartridge which is handled as a replacement part because the maintainability is remarkably improved.

FIG. 6 is a conceptual diagram for explaining an output image in the first embodiment.
An undercoat layer, a charge generation layer, a charge transport layer, and a protective layer were applied in this order on an aluminum drum (conductive support) having a diameter of 30 mm, and then dried, followed by drying. A photoreceptor comprising a 15 μm charge generation layer, a 22 μm charge transport layer, and a protective layer of about 4.5 μm was prepared. At this time, the coating of the protective layer was performed by a spray method, and the others were performed by a dip coating method. 22.5% by mass of alumina having an average particle size of 0.21 μm was added to the protective layer.
Supplied by a charging roller manufacturer as a charging roller for a black photoconductor unit of imagio Neo C385 (tandem color image forming apparatus, linear speed of photoconductor: modified to 205 mm / second, writing light resolution 600 dpi, manufactured by Ricoh) Three types of charging roller prototypes were evaluated. The charging roller was manufactured by attaching a conductive rubber mainly composed of epichlorohydrin rubber and conductive carbon to a stainless steel cylinder, and had a rubber hardness (type A) of 73. The diameter of the charging roller was 11.5 mm. A gap tape (base polymer is polyester) having a width of 10 mm and a thickness of 45 μm was attached to a stainless steel cylindrical portion outside the charging roller at a position of 13 mm. A charging roller is disposed directly above the photosensitive member, and the charging roller is pressed against the photosensitive member with a spring, and the DC voltage of −600 V is applied to a frequency of 1280 Hz between the photosensitive member and the charging roller under the condition that the photosensitive member and the charging roller are not rotated. Then, an alternating voltage with an amplitude of 1050 V was superimposed and applied for 10 minutes. Two white streak discharge traces were formed on the charging roller and the photoreceptor. The average width of the two lines was 0.51 mm and 0.47 mm, respectively. The average distance between the two lines was 0.35 mm.
The charging roller and the photosensitive member of each of the photosensitive units of black, cyan, yellow, and magenta are replaced with new ones. Between the charging roller and the photosensitive member of each photosensitive unit, a direct current voltage of −600 V is applied to an alternating current having a frequency of 1600 Hz and an amplitude of 1050 V. When black, cyan, and magenta halftone images as shown in FIG. 4 were output under charging conditions in which voltages were applied in a superimposed manner, high-quality images were obtained for all color images.

In the first embodiment, the resolution of the writing light of the image forming apparatus is modified to 1200 dpi, and a charging roller is manufactured using gap tapes of 40 μm and 26 μm, and the photoreceptor and the charging roller are not rotated as in the first embodiment. Under the conditions, an AC voltage having a frequency of 1450 Hz and an amplitude of 1050 V was superimposed on a DC voltage of −600 V between the photosensitive member and the charging roller and applied for 10 minutes. Two white streak discharge traces were formed on the charging roller and the photoreceptor. The average widths of two streaks with a gap tape of 40 μm were 0.55 mm and 0.53 mm, respectively, and the average distance between the two streaks was 0.45 mm. On the other hand, when the gap tape was 26 μm, the average widths of the two lines were 0.57 mm and 0.54 mm, respectively, and the average distance between the two lines was 0.60 mm.
A photoconductor unit using a charging roller with a gap tape of 40 μm is set in a magenta station, a photoconductor unit using a charging roller with a gap tape of 26 μm is set in a black station, and two A4 images as shown in FIG. A total of 50000 sheets were output. At this time, the AC frequency applied to the charging roller of the black photosensitive unit and the magenta photosensitive unit was 1450 Hz, and the AC frequency applied to the charging rollers of the other color photosensitive units was 1600 Hz.
After forming 50,000 images, a black, cyan, and magenta halftone image as shown in FIG. 4 was output.
High-quality images were obtained for cyan and magenta images, but streaky abnormal images were seen for black images. Observation of the charging roller of the photoconductor unit for black revealed that deposits were streaked at locations corresponding to streaky abnormal images.

A material made mainly of ABS resin, carbon and ionic conductive material is laminated on a stainless steel cylinder, and a charging roller having a diameter of 13 mm or 22.6 mm is used. The outside of the charging roller is made of polyvinylidene fluoride having a diameter of 13.05 mm. A cap roller was provided to provide a gap between the photoreceptor and the charging roller.
As in Example 1, under the condition that the photoconductor and the charging roller were not rotated, an AC voltage having a frequency of 1350 Hz and an amplitude of 1000 V was superimposed between the photoconductor and the charging roller for 10 minutes. Two white streak discharge traces were formed on the charging roller and the photoreceptor. The average widths of the two lines were 0.58 mm and 0.60 mm, respectively, and the average distance between the two lines was 0.34 mm.
A new charging roller and a photoconductor are set in all photoconductor units, and an AC voltage with a frequency of 1350 Hz and an amplitude of 1000 V is superimposed and applied between the photoconductor and the charge roller, and a line of the photoconductor is applied. When a halftone image of each color was formed at a speed of 185 mm / sec, high-quality images were obtained for all color images.

It is a schematic diagram for demonstrating the discharge trace which arises on a photoconductor. It is a conceptual diagram which shows the charge state by the uniform charge distribution in a photoreceptor surface. It is a conceptual diagram which shows the charge state by non-uniform charge distribution. 1 is a conceptual diagram illustrating an image forming apparatus to which the present invention is applied. It is a figure which shows one structural example for making a fine gap between a charging roller and a photoreceptor surface. 6 is a conceptual diagram for explaining an output image in Embodiment 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 5 Charging apparatus 7 Developing apparatus 13 Charging roller 14 Power supply G Minute gap w1 Width of charging area 1 w2 Width of charging area 2 ws Width of non-discharge area

Claims (7)

  In an image forming apparatus comprising at least a photoconductor, a charging roller that is not in contact with the photoconductor, and a power source that charges the surface of the photoconductor by applying an AC voltage in which a DC voltage is superimposed on the charging roller, The photosensitive member is not rotated, and a voltage from the power source is applied to the charging roller for a certain period of time, so that the discharge traces in the image forming area generated on the photosensitive member are continuous with two stripes in the longitudinal direction of the photosensitive member. The average value of the widths of the two discharge marks obtained by setting the distance between the photosensitive member and the charging roller, the voltage value of the DC voltage, and the voltage value of the AC voltage is w0 (mm). When the linear velocity at the time of image formation of the photoconductor is v (mm / second) and f0 = v / w0, the frequency f (Hz) at the time of image formation of the AC voltage is 2.2 times or more of f0. , 13 times or less Image forming apparatus.   2. The image forming apparatus according to claim 1, wherein ws is 1% or more and 33% or less of 2 × w0, where ws (mm) is the width of the gap between the two stripes. Image forming apparatus.   3. The image forming apparatus according to claim 1, wherein the predetermined period of time is set to (fs / 1000 to fs / 10), where fs is a design alternating frequency.   4. The image forming apparatus according to claim 1, wherein a linear velocity at the time of image formation of the photoconductor is v ≧ 150. 5.   5. The image forming apparatus according to claim 1, wherein an outer diameter of the charging roller is 9 mm or more and 25 mm or less. 6.   6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a tandem type.   7. The image forming apparatus according to claim 1, wherein the maximum resolution of an image that can be formed is 1000 dpi or more.

Images