JP2007025548A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a retransfer (image void) problem due to poor release by improving paper releasability from a photoreceptor drum. <P>SOLUTION: A minute-dot toner image is formed on a non-image part (white ground part) other than a toner image part as image information on a recording paper, and a formation position of the minute-dot toner image is controlled in accordance with the position of the toner image as image information so that it is not formed adjacently to the toner image as image information. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus (copier, facsimile, printer, etc.), and more particularly to a digital image forming apparatus.

  In general, in an electrophotographic image forming apparatus, a photosensitive member is charged by a charging device, and is exposed based on image information by an exposure device to form an electrostatic latent image on the surface of the photosensitive member. The toner is developed by a developing device to form a toner image as image information on the surface of the photoreceptor. After the recording paper is picked up from the recording paper cassette, the toner image on the photosensitive member is electrostatically transferred to the recording paper by the transfer device in the transfer unit. Thereafter, the recording paper carrying the toner image is separated from the photoreceptor and conveyed to a fixing device, and the toner image is fixed on the recording paper by heat and pressure. After the transfer residual toner on the photoconductor is removed by a cleaning device arranged downstream of the transfer portion on the surface of the photoconductor, the photoconductor is charged again by the charging device to prepare for the next image forming operation.

  Separation of the photoconductor from the recording paper is performed when the rigidity of the recording paper exceeds the electrostatic attraction between the photoconductor and the recording paper. After the toner image is transferred, a method of applying a bias having a polarity opposite to the transfer bias by the charge eliminating device to neutralize the charge on the recording paper and improve the separation property is adopted.

In order to reliably separate the recording paper, there is a method that employs a separation claw that mechanically separates the recording paper adsorbed on the photosensitive member.
Japanese Patent No. 3117153 JP-A-5-241419 JP-A-11-52758 JP 2004-118076 A JP 2004-151588 A

  In general, in order to separate the recording paper from the photoconductor, the radius of curvature of the photoconductor is reduced, that is, the drum diameter of the photoconductor is reduced so that the rigidity of the recording paper is easily applied. In this case, it is preferable to reduce the radius of curvature at the transfer portion.

  However, along with the recent increase in the speed of image forming apparatuses, it is necessary to increase the size of the charging device, the developing device, the cleaning device, and the like, and to increase the diameter of the drum of the photosensitive member. Therefore, the radius of curvature of the photosensitive member is increased, the recording paper conveyance speed is increased, and the separation between the photosensitive member and the recording paper is further deteriorated.

  In order to improve the separability, if the neutralization by the static eliminator is strengthened, the toner image transferred onto the recording paper cannot be electrostatically held on the recording paper, and the toner image transferred onto the recording paper at the transfer section will not be retained. Then, there is a problem of retransfer that is transferred onto the photosensitive member again and white spots occur on the toner image on the recording paper.

  In addition, if the static elimination by the static eliminator is weakened, the separation between the photosensitive member and the recording paper is reduced, and the static elimination time by the static eliminator becomes long. The toner image transferred by the transfer unit onto the recording paper without being electrically held can be transferred again onto the photosensitive member, resulting in a problem of retransfer that causes white spots on the toner image on the recording paper.

  Therefore, it is necessary to set the static elimination condition setting value (voltage value or current value) of the static elimination device within a predetermined range determined by the upper limit value and the lower limit value.

  In addition, when the separability is further lowered, the leading edge of the recording paper enters the cleaning device, and a jam that interrupts image formation occurs.

  In order to prevent the recording paper from entering the cleaning device, when the recording paper is forcibly separated from the photoconductor by the separation claw, the separation claw comes into contact with the photoconductor. When the separation performance is lowered, the toner adhering to the separation claw comes into contact with the leading end portion of the recording paper, and the recording paper leading end portion is stained.

  In addition, when an unnecessary toner called fog is attached to a non-image portion (white background portion) on the photosensitive member to improve separation, the amount of fog toner to be attached on the photosensitive member (hereinafter referred to as fog amount). Cannot be controlled stably. That is, the fog on the photosensitive drum is also transferred at the same time as the toner image and fixed on the recording sheet. Therefore, the fog amount on the recording sheet cannot be stably controlled, and if the fog amount is increased to improve the separation property. If a non-image portion on the recording paper is stained with fog toner and an image defect occurs, and the amount of fog is reduced, a problem occurs in that the separability is lowered.

  As shown in FIG. 2, the amount of fog is determined by the charging potential of the non-image area of the photoconductor (in the case of reversal development, non-exposed area potential: VD) and the developing bias applied to the developing sleeve of the developing device. It is determined by the absolute value Vback (= | VD−Vdc |) of the difference from the DC voltage (Vdc). FIG. 2 shows the amount of fog on the recording sheet on the vertical axis and Vback on the horizontal axis. The amount of fog on the recording paper shows the difference in reflection density between the unused recording paper and the non-image area (white area) of the recording paper on which the image has been formed. It shows that you are doing. The fogging amount on the recording paper is preferably about 2% so that the separation is good and the fogging amount on the recording paper does not cause an image defect.

  However, a portion where the fog value on the recording paper is about 2% is a portion where the curve changes abruptly in the graph shown in FIG. 2, such as variations in the image forming apparatus (development DC bias value or non-image of the photoreceptor). Due to the fluctuation of the partial potential, etc., there is a problem that even if the Vback slightly fluctuates, an image defect in which the fog amount on the recording paper increases or a fogging amount on the recording paper decreases and a separation defect occurs. Therefore, there is a problem that the fog amount on the photosensitive member, that is, the fog amount on the recording paper cannot be stably controlled.

  On the other hand, a method of forming a dot toner image on a non-image portion (white background portion) has been proposed as a method for improving the separation between the photosensitive member and the recording paper.

  In Patent Document 1, a dot toner image different from image information is arranged at the leading end of a recording sheet, and toner is interposed as spacer particles between the photosensitive member and the recording sheet to improve the separation property. However, in order to form a dot toner image on the non-image portion only at the front end portion, there is a problem that only the front end portion is recognized as having a lot of fog, and the white background portion of the image background is not uniform, causing a sense of incongruity. . Further, the re-transfer problem due to the separation failure occurs not only at the front end portion of the recording paper but also at the central portion of the recording paper. Further, since the light amount at the time of dot toner image formation is made smaller than the image information light amount, a portion where the photosensitive member surface potential of the exposed portion is unstable is used (the relationship curve between the light amount and the photosensitive member surface potential changes rapidly). Since the dots formed in the non-image area cannot be formed stably, there is a problem that the amount of fog is unstable, that is, the separation property is unstable.

  In particular, a toner image (original image) based on image information and a dot toner image are adjacent to each other, and the original image is recognized with unevenness. The toner of the original image moves to the dot toner image portion and disturbs the original image. There was a big problem.

  Further, although the purpose is not to improve the separability, a method for forming a dot toner image in a non-image portion has been proposed.

  Japanese Patent Application Laid-Open No. H10-228707 forms a low-density yellow pattern on a non-image portion to prevent talc from adhering to a photoconductor. However, when this is applied to a black-and-white image forming apparatus, it becomes a problem because it is recognized as background dirt on the recording paper, and the pitch between dots is a regular cycle of 50 dots, so that a moire image (cycle As a typical image), there is a problem that dots are periodically emphasized.

  In particular, as a method for forming a dot toner image, the original image and the dot toner image are not adjacent to each other in the main scanning direction, but the original image and the dot toner image are adjacent to each other in the sub-scanning direction. There is a big problem that the original image is recognized as uneven, and the toner of the original image moves to the dot toner image portion and disturbs the original image.

  Japanese Patent Application Laid-Open No. H10-228561 forms dot toner images uniformly dispersed to prevent linear velocity fluctuations on the surface of the photoreceptor and the surface of the intermediate transfer member, thereby preventing image displacement. However, since it is a large dot toner image with a dot diameter of 150 to 300 μm, in the case of a dot toner image of a color other than yellow, for example, a black color, it cannot be recognized as fog of a non-image portion, but is recognized as a dot image and defective. The problem of becoming an image occurs.

  In particular, when an original image and a dot toner image are adjacent to each other, such as when a dot toner image is formed over the image information, the original image is recognized as uneven, and the toner of the original image moves to the dot toner image portion. There was a big problem of disturbing the original image.

  In Patent Documents 4 and 5, as in Patent Document 3, dot toner images are dispersedly formed (additional images are formed) to prevent fluctuations in the linear velocity between the photosensitive member surface and the intermediate transfer member surface. This is to prevent image streaks. However, when the dot toner image is a color toner other than yellow, for example, a black dot toner image, the occurrence of moire or the oblique line image can be recognized because of the dot toner image or the oblique line image formed periodically. Problems occur.

  In particular, when an original image and a dot toner image are adjacent to each other, such as when a dot toner image is formed over the image information, the original image is recognized as uneven, and the toner of the original image moves to the dot toner image portion. There was a big problem of disturbing the original image.

  Therefore, in view of the above problems, an object of the present invention is to form a fine dot toner image on a non-image portion (white background portion) photoreceptor other than image information, and between the photoreceptor or intermediate transfer member and the recording paper. By causing the toner to act as spacer particles, the separation of the recording paper from the photosensitive member or intermediate transfer member is improved, and the problem of retransfer (image blanking) due to poor separation is prevented. ) And the fine dot toner are adjacent to each other, and an image forming apparatus that prevents the problem of disturbing the original image is provided.

  A second object of the present invention is to form a fine dot toner image that does not cause moiré, does not recognize as dots (recognizes as uniform fog on the entire surface), does not generate partial fog, or the like. An object of the present invention is to provide an image forming apparatus that forms a fine dot toner image in which the number of images (fogging amount) can be arbitrarily adjusted.

  The above object is achieved by the following image forming apparatus according to the present invention.

  (1) The photosensitive member is charged by a charging device, the photosensitive member is exposed to light based on image information by an exposure device, an electrostatic latent image is formed on the surface of the photosensitive member, and the electrostatic latent image is developed by a developing device. Development is performed to form a toner image as image information on the surface of the photosensitive member, and the toner image is transferred to a recording sheet by a transfer device, or the toner image is transferred to an intermediate transfer member by a primary transfer device, and then intermediate In an image forming apparatus for transferring a toner image on a transfer body onto a recording sheet by a secondary transfer device, conveying the recording sheet carrying the toner image to a fixing device, and fixing the toner image on the recording sheet, A fine dot toner image is formed on a non-image portion (white background portion) other than the toner image portion as image information of the image, and the fine dot toner image is not formed adjacent to the toner image as image information. Depending on the toner image position as information, an image forming apparatus and controls the formation position of the fine dot toner images.

  (2) The photosensitive member is charged by a charging device, the photosensitive member is exposed to light based on image information by an exposure device, an electrostatic latent image is formed on the surface of the photosensitive member, and the electrostatic latent image is developed by a developing device. Development is performed to form a toner image as image information on the surface of the photosensitive member, and the toner image is transferred to a recording sheet by a transfer device, or the toner image is transferred to an intermediate transfer member by a primary transfer device, and then intermediate In an image forming apparatus for transferring a toner image on a transfer body onto a recording sheet by a secondary transfer device, conveying the recording sheet carrying the toner image to a fixing device, and fixing the toner image on the recording sheet, A fine dot toner image is formed in a non-image portion (white background portion) other than the toner image portion as image information of the image, and the fine dot toner image has a predetermined plural pixel unit as one unit, An image forming apparatus, and forming a pixel position of the central portion excluding the outer peripheral portion of at least the minimum pixels Te.

(3) The size (number of dots forming pixels) of the minute dot toner image formed in the non-image portion is 1200 dpi 2.25 dots (2.25 pixels) or less, that is, 1100 μm ² or less. The image forming apparatus according to (1) or (2).

  (4) For the minute dot toner image formation position, a dot formation pattern is selected for each unit by a random number from a plurality of different dot formation patterns corresponding to a predetermined number of dot formation pixels at the dot formation pixel position in one unit. The image forming apparatus according to any one of (1) to (3), wherein the image forming apparatus is determined by

  (5) In the minute dot toner image formation, at one dot unit pixel position within the one unit, “dot formation” and “dot formation” are set as one unit with a random number based on a predetermined frequency (0 to 100%). The image forming apparatus according to any one of (1) to (3), wherein the image forming apparatus is determined by selecting each time.

  (6) In the minute dot toner image formation, at one dot unit pixel position within the one unit, “dot formation” and “no dot formation” are set as one unit with a random number based on a predetermined frequency (0 to 100%). The above is characterized in that it is determined by selecting a dot formation pattern by a random number for each unit for dot formation from a plurality of different dot formation patterns corresponding to the number of dot formation pixels of one unit. The image forming apparatus according to any one of 1) to (3).

  (7) The number of fine dot toner images in the non-image area on the recording paper is determined by a combination of the number of dots formed by one unit and the frequency (0 to 100%). This is an image forming apparatus.

  (8) Depending on the image forming mode (for example, copy / print, etc.), or the recording paper type (for example, thick paper / thin paper / second original paper (tracing paper) / recycled paper / colored paper / OHT), or non-environment The image forming apparatus as described in (7) above, wherein the number of dot forming pixels of one unit of the minute dot toner image formed in the image portion and the frequency (0 to 100%) are variable.

  (1) According to the first aspect of the present invention, a toner image (original image) based on image information and a minute dot toner image are adjacent to each other, and the original image is recognized with unevenness. A problem that the original image is disturbed by moving to the toner image portion can be prevented, and a separation failure between the photosensitive member or the intermediate transfer member and the recording paper can be prevented, and a clear image can be obtained.

  (2) According to the second aspect of the present invention, the toner image (original image) based on the image information and the minute dot toner image are adjacent to each other, and the original image is recognized with irregularities. The problem that the original image is disturbed by moving to the toner image portion is prevented, and furthermore, the small dot toner images formed in the non-image portion are adjacent to each other to form a large dot, which cannot be visually recognized as fog, It is possible to prevent the problem of being recognized as dots, prevent poor separation between the photosensitive member or the intermediate transfer member and the recording paper, and obtain a clear image.

  (3) According to the invention described in claim 3, it is possible to prevent a problem that a minute dot toner image formed in a non-image portion cannot be visually recognized as fog and is recognized as a dot.

  (4) According to the invention described in claim 4, it is possible to prevent the problem of moire in which minute dot toner images formed in a non-image part are periodically arranged, and the shading of the non-image part is periodically generated.

  (5) According to the fifth aspect of the present invention, the unit of minute dot toner images formed in the non-image portion is periodically arranged, and the density of the fog in the non-image portion is periodically generated (4 ) Can prevent the problem of moire at a lower frequency.

  (6) According to the invention described in claim 6, the fine dot toner image formed in the non-image part is periodically arranged, and the problem of moire in which the density of the fog in the non-image part is periodically generated can be prevented. Furthermore, one unit unit of the fine dot toner image formed in the non-image portion is periodically arranged, and the problem of moire at a lower frequency than the above, in which the density of the fog in the non-image portion is periodically generated, can be prevented.

  (7) According to the seventh aspect of the invention, the number of fine dot toner images formed on the non-image portion, that is, the fog amount of the non-image portion can be easily and arbitrarily adjusted.

  (8) According to the invention described in claim 8, according to the image forming mode, the type of recording paper, the environment, etc., the optimum number of fine dot toner images to be formed on the non-image area, that is, the fog amount of the non-image area is easy. In addition, since it can be arbitrarily adjusted, even if various conditions fluctuate, it is possible to stably prevent a separation failure between the photosensitive member or the intermediate transfer member and the recording paper and obtain a clear image.

  As described above, according to the present invention, the separation performance between the photosensitive member or the intermediate transfer member and the recording paper is stably maintained, and the fine dot toner image is controlled so as not to affect the original image. It is possible to provide an image forming apparatus provided with a method for forming a fine dot toner image in a non-image part capable of obtaining a clear image.

  Embodiments of the present invention will be described with reference to FIGS. In addition, in these drawings, the same member is attached | subjected the same code | symbol and the overlapping description is abbreviate | omitted.

  A first embodiment according to the present invention will be described with reference to FIGS. 1 and 3 to 18.

  FIG. 1 is an example of an image forming apparatus 100 of a reversal development system (IAE: Image Area Exposure) for explaining the first embodiment of the present invention.

  As shown in FIG. 1, in the image forming apparatus 100, a photosensitive drum 1 as a photosensitive member is rotatably attached, and rotates clockwise as indicated by an arrow. In the process of rotating the photosensitive drum 1, the surface of the photosensitive drum 1 is charged uniformly and uniformly, for example, by passing through the charging device 2 (for example, charging potential: + 400V).

  Next, the exposure device 3 irradiates laser light corresponding to the image information (image portion), thereby forming an electrostatic latent image on the photosensitive drum 1 (for example, laser exposure portion charging potential: +50 V).

  Next, the electrostatic latent image on the photosensitive drum 1 is a positively charged toner T as a developing sleeve 4a (for example, DC: +250 V, AC: 1200 Vpp) to which a bias of the developing device 4 is applied rotates in the direction of the arrow. As a result of the reversal development, a toner T image is formed on the portion of the photosensitive drum 1 irradiated with the laser light. When the toner T image on the photosensitive drum 1 reaches the transfer device 5, the transfer device 5 generates a negative corona discharge, and is electrostatically transferred onto the recording paper P. A neutralization device 6 is arranged in the vicinity of the downstream of the transfer device 5. The neutralization device 6 is such that when the recording paper P is negatively charged due to the transfer of the toner T image, the recording paper P is positively charged (particularly, the photosensitive drum 1). This is to prevent the negative charge of the recording paper P from being absorbed by the AC corona discharge superimposed with the positive DC voltage. .

  Accordingly, the recording paper P to which the toner T image has been transferred is neutralized by passing through the neutralization device 6, separated from the photosensitive drum 1, and the recording paper P carrying the toner T image is then conveyed to the fixing device 8. Is done. When the recording paper P carrying the toner T image passes through the fixing device 8, the recording paper P receives heat and pressure, and the toner T image is fixed on the recording paper P.

  On the other hand, the photosensitive drum 1 that has completed the transfer process, after the transfer residual toner on the photosensitive drum 1 is removed by the cleaning device 7, is uniformly charged again by the charging device 2 to prepare for the next image formation.

  In this embodiment, on the surface of the photosensitive drum 1, a non-image portion (white background portion other than the toner T image) of the recording paper P corresponding to the recording paper P is irradiated with laser light of minute dots different from the image information. The developing device 4 develops the minute dots and attaches a minute dot toner image. This fine dot toner image is interposed as spacer particles between the recording paper P and the photosensitive drum 1, weakens the electrostatic adsorption force between the recording paper P and the photosensitive drum 1, and separates the recording paper P from the photosensitive drum 1. make it easier.

  Therefore, the minute dot toner image needs to be made almost inconspicuous visually, like the unnecessary toner called fog that adheres to the non-image portion on the recording paper P, and the image information on the recording paper P is It is necessary not to affect the toner T image (original image) based thereon, and further, it is necessary to improve the separation between the photosensitive drum 1 and the recording paper P.

  The fine dot toner image forming method will be described.

  The present embodiment is an image forming apparatus capable of outputting a resolution of 1200 dpi in the main scanning direction and 1200 dpi in the sub-scanning direction. Due to the configuration of the apparatus, the minute dots are 0 in the main scanning direction as shown in FIG. It can be formed in units of .5 dots (0.5 pixels) and 1 dot (1 pixel) of 1200 dpi in the sub-scanning direction.

  Further, in the non-image portion, a unit of 4 dots (4 pixels) × 4 dots (4 pixels) = 16 dots (16 pixels) is one unit, and a predetermined dot in the 16 dots (16 pixels) unit is a minute dot toner. The image is formed as an image.

  A black portion in FIG. 3 shows a minute dot toner image. When the interval between the original images, that is, the non-image portion is smaller than one unit (= 16 pixels), the configuration is such that minute dots are not formed.

  First, it has been found that if the fine dot toner image is 4 dots (4 pixels) of 1200 dpi as shown in FIG. 4, it is visually recognized as a dot and becomes conspicuous in the non-image portion. Accordingly, in the image forming apparatus of 600 dpi, as the minute dots, in the image forming apparatus in which the minimum formed dot is equivalent to one dot (one pixel) of 600 dpi, that is, four dots (4 pixels) of 1200 dpi, the minute dots of this embodiment are used. It has been found that the improvement in separability by the toner image cannot be applied.

  Further, it was also found that the minute dot toner image is visually recognized as a dot even with 3 dots (3 pixels) of 1200 dpi as shown in FIG. 5 and is conspicuous in the non-image portion (white background portion).

  Next, a minute dot toner image cannot be formed by two dots of 1200 dpi (two pixels: about 22 μm × about 44 μm) as shown in FIG. 6 and the image forming apparatus used in this embodiment, but another image forming apparatus In FIG. 7, the 1.5-dot square as shown in FIG. 7, that is, 2.25 dots (2.25 pixels: about 33 μm × about 33 μm), cannot be recognized as dots, and the non-image portion (white background) on the recording paper P As with fog toner that normally adheres to the part), it was found that it was hardly noticeable visually.

Therefore, it is necessary that the fine dots be 1200 dpi 2.25 dots (2.25 pixels) or less, that is, an area of about 1089 μm ² or less.

  If it is 2 dots (2 pixels) of 1200 dpi as shown in FIG. 6, it is not visually noticeable. Therefore, each of the 4 units shown in FIG. ) Are arranged as shown in FIG. 8B in the non-image area, and when the minute dot toner images are arranged adjacent to each other, they are recognized as dots and are visually noticeable in the non-image area. appear.

  Therefore, in order to prevent the formation of large dots due to the combination of the units, as shown in FIG. 8C, only 9 dots (9 pixels) indicated by diagonal lines are included in one unit (= 16 pixel units). It is necessary to form a fine dot toner image.

  For example, a minute dot toner image is formed on two pixels in the hatched portion as shown in FIG. 9A so that a minute dot toner image is formed only on the nine dots (9 pixels) in the hatched portion shown in FIG. In this case, it was possible to prevent the formation of large dots by combining the units. However, when one unit is arranged in the non-image portion as shown in FIG. 9B, the fine dot toner image in the non-image portion is compared to the toner image (original image) M formed based on the image information. There is a problem in that the original image M is recognized as an unevenness adjacent to the original image M, or the original image M is disturbed by the toner of the original image M moving to the adjacent non-image portion minute dot toner image portion. appear.

  Therefore, in order to prevent the minute dot toner image of the non-image part from being adjacent to the original image M, as shown in FIG. 9C, only 4 dots (4 pixels) indicated by diagonal lines in one unit. It is necessary to form a fine dot toner image.

  In addition, when the minute dot toner images in the non-image portion are periodically arranged, if it is about 2 pixels or less, it cannot be visually recognized as a dot and is recognized as a fog, but a periodic shading occurs in the fog. A phenomenon called moire occurs. In order to prevent this moire, a method that does not periodically arrange minute dot toner images in the non-image area is necessary.

  Therefore, in this embodiment, as a minute dot toner image in one unit of a non-image part, for example, when 0.5 dots (0.5 pixels) are formed, a minute dot toner image is randomly generated from the eight patterns shown in FIG. A method of selecting a formation pattern is employed. The selection by random numbers is such that one of the eight patterns is randomly selected by the processing means (not shown) of the image forming apparatus, that is, for example, the pattern is selected by rolling the dice by the processing means (not shown). It has become.

  For example, when 1 dot (1 pixel) is formed as a minute dot toner image, one pattern is selected from 4 patterns shown in FIG. 11 by random numbers, and when 1.5 dots (1.5 pixels) are formed, FIG. One pattern is selected from the 12 patterns indicated by. At the time of 1.5 dot formation, 24 patterns shown in FIG. 12B can be considered as combinations, but 12 patterns shown in FIG. This combination of patterns may be arbitrarily set according to the image forming apparatus or the like.

  When two dots (two pixels) are formed, one pattern is selected from the six patterns shown in FIG. Further, the size of the minute dot toner image in one unit may not be one type, and a plurality of types may be mixed.

  For example, as shown in FIG. 14, one pattern is selected by random numbers from 8 patterns combining 0.5 dots and 1 dot. As shown in FIG. 15, 1 pattern is selected from 8 patterns combining 1 dot and 1.5 dots. Selection may be made arbitrarily by selecting with a random number, or selecting one pattern with a random number from eight patterns combining 1.5 dots and 2 dots as shown in FIG.

  Therefore, in order to prevent the minute dot toner images from being periodically arranged, that is, to prevent the occurrence of moire, a pattern is selected with a random number from a plurality of minute dot toner image formation patterns, and the minute dot toner images are randomly formed. There is a need.

  Furthermore, in order to adjust the number of fine dot toner images formed in the non-image portion, that is, the fog amount, it is preferable to adjust the frequency of selecting whether or not to form a fine dot toner image. As the frequency, when a predetermined frequency is selected, a processing unit (not shown) of the image forming apparatus may or may not form a minute dot toner image in the one unit with a random number according to the predetermined frequency. Select at random. For example, when 25% is selected as the predetermined frequency, 1 is formed, 2: is not formed, 3: is not formed, 4: is not formed, and 1 to 4 in random numbers for each unit of the non-image portion. Is processed by a processing means (not shown) so as to select.

  That is, for example, a processing unit (not shown) rolls 1 to 4 dice for each unit, and selects whether or not to form a fine dot toner image in that unit. According to this method, the unit that forms the fine dot toner image and the unit that does not form the fine dot toner image are not periodically arranged. Therefore, the moire generated by the periodic arrangement of the fine dot toner images described above. However, it is possible to prevent moiré that occurs at a lower frequency.

  FIG. 17 shows an example of the fog amount corresponding to the size (dot system) and frequency of one unit of minute dot toner image in the non-image area. The fog amount is the same as the fog amount measurement method described above. As shown in FIG. 17, when no fine dot toner image is formed in the non-image area, the fog amount is 1%, and the fog amount is small, resulting in poor separation and the above-described retransfer problem. .

  As described in the present embodiment, the fog amount is reduced to about 2% by selecting the frequency 50% of the 0.5 to 1 dot system (using the combination pattern of 0.5 dot and 1 dot shown in FIG. 14). Thus, the re-transfer problem can be prevented, and further, it can be recognized as a uniform fog visually, and a clear image that does not affect the original image and does not generate moire can be obtained.

  Actually, in the case of the above condition, in each unit of the non-image part, the processing means (not shown) of the image forming apparatus performs 1: dot formation from the frequency 50% for each unit, 2: do not form dots. When 1 and 2 are selected with random numbers and 1: dot formation is selected, the operation of selecting one pattern with random numbers from the 8 patterns shown in FIG. A dot toner image is formed.

  Further, as an image forming mode, for example, in an image forming apparatus in which Vback is different between the copy mode and the print mode, the amount of fog when no minute dot toner image is formed is different between the copy mode and the print mode. This is the case where the Vback is made smaller in the print mode in order to increase the line width than in the copy mode.

  In this case, for example, FIG. 17 shows an example in the print mode, and FIG. 18 shows an example in the copy mode. When a minute dot toner image is not formed at all, the fog amount in the print mode in FIG. Compared to 1%, the fog amount is 0.5% in the copy mode of FIG. At this time, in order to ensure separation, in the print mode of FIG. 17, the fog amount is set to about 2% by selecting the frequency of 0.5 to 1 dot system to 50%, and in the copy mode of FIG. By selecting a frequency of 60% for one dot system, the fog amount is about 2%, preventing re-transfer problems due to poor separation in both modes, and can be recognized as uniform fog on the eyes, affecting the original image. And a clear image with no moire could be obtained.

  As described above, the fine dot toner image forming method selection according to the image forming mode (the method of arbitrarily selecting the frequency and the dot system) can be manually input to the image forming apparatus or computer, or the image can be formed on the image forming apparatus. A method of detecting a mode (not shown) and automatically selecting the image forming apparatus may be used.

  In addition, if a method of arbitrarily selecting the frequency and the dot system according to the type of recording paper is used, it is possible to prevent a retransfer problem due to poor separation according to various paper types.

For example, in the image forming apparatus shown in FIG. 17, in the case of a recording sheet of 64 g / m ² or more, the fogging amount is about 2% in the 0.5 to 1 dot system with the selection frequency of 50% and less than 64 g / m ^2. In the case of a thin recording paper, the rigidity of the recording paper is small, and separation between the photosensitive drum 1 and the recording paper P is severe. Therefore, a frequency of 0.5 to 1 dot system of 75%, or 1 dot of 50% frequency. If the system is configured to have a fog amount of about 2.5%, it is possible to prevent poor separation even with thin recording paper. In this way, by adjusting the amount of fog according to the type of recording paper (selecting the frequency and dot system arbitrarily), the re-transfer problem due to poor separation can be prevented even in various types of recording paper, and further visually A clear image that can be recognized as uniform fog, does not affect the original image, and does not generate moire can be obtained.

  The fine dot toner image forming method selection according to the type of recording paper (method for arbitrarily selecting the frequency and dot system) is a method of manually inputting to the image forming apparatus or computer, or the recording paper type is detected by the image forming apparatus. A method in which means (not shown) is mounted and the image forming apparatus automatically selects may be used.

  Further, a configuration in which a plurality of fine dot toner image forming methods such as normal recording paper, thin recording paper, and thick recording paper may be selected.

  Furthermore, in an image forming apparatus in which the amount of fog changes depending on the environment in which the image forming apparatus is installed, a minute dot toner image forming method is arbitrarily selected according to the environment, that is, the frequency and the dot system are arbitrarily selected. By using the selection method, it is possible to prevent a retransfer problem due to poor separation according to various environments.

  For example, when the installation environment of the image forming apparatus is a normal environment (temperature: 23 ° C., relative humidity: 50%), as shown in the example of FIG. The fog amount of about 2% is used in the 0.5 to 1 dot system with the frequency of 50%.

  For example, when the installation environment of the same image forming apparatus is a high-temperature and high-humidity environment (temperature: 30 ° C., relative humidity: 70%), as shown in the example of FIG. % And the fog amount is smaller than the normal environment, the fog amount of about 2% is used in a one-dot system with a frequency of 60%.

  In this way, by adjusting the amount of fog according to the environment (selecting the frequency and dot system arbitrarily), the re-transfer problem due to separation failure is prevented even in various environments, and furthermore, the fog is visually uniform. A clear image that can be recognized, does not affect the original image, and does not generate moire can be obtained.

  The fine dot toner image forming method selection according to the installation environment of the image forming apparatus is a method of manually inputting to the image forming apparatus or the computer, or means (not shown) for detecting the environment (temperature, humidity) in the image forming apparatus. A method of mounting and automatically selecting by the image forming apparatus may be used.

Further, in the case of a thin recording paper of less than 64 g / m ^{2 in} a high temperature and high humidity environment (temperature: 30 ° C., relative humidity: 70%), the moisture of the recording paper is absorbed to reduce the rigidity of the recording paper, and the separation becomes severe. As shown in an example of FIG. 18, when the above-described configuration example is arbitrarily combined, such as using a fog amount of about 3% in a 1.5 dot system with a frequency of 60%, the separation can be performed more accurately according to the situation. The re-transfer problem due to defects can be prevented, and further, a clear image that can be recognized visually as uniform fog, does not affect the original image, and does not cause moiré can be obtained.

  A second embodiment according to the present invention will be described with reference to FIGS.

  FIG. 19 is an example of a regular development system (BAE: Background Area Exposure) image forming apparatus 101 for explaining the second embodiment of the present invention.

  In the first exemplary embodiment, the description has been made on the reversal developing system (IAE: Image Area Exposure), that is, the image forming apparatus in which the image is formed (the toner adheres) on the portion exposed by the exposure device on the surface of the photoreceptor.

  On the other hand, the present embodiment also relates to a regular development system (BAE: Background Area Exposure), that is, an image forming apparatus in which an image is formed on a portion that is not exposed by the exposure device on the surface of the photosensitive member (toner adheres). By applying the present invention, it will be described that the same effect as in the first embodiment can be obtained.

  As shown in FIG. 19, in the image forming apparatus 101, a photosensitive drum 1 as a photosensitive member is rotatably attached, and rotates clockwise as indicated by an arrow. In the process of rotating the photosensitive drum 1, the surface of the photosensitive drum 1 is charged uniformly and uniformly, for example, by passing through the charging device 2 (for example, charging potential: + 400V). Next, the exposure device 3 irradiates laser light corresponding to the image information (image portion), thereby forming an electrostatic latent image on the photosensitive drum 1 (for example, laser exposure portion charging potential: +50 V).

  Next, the electrostatic latent image on the photosensitive drum 1 is generated by the developing sleeve 4a (for example, DC: + 200V, AC: 1200Vpp) to which the bias of the developing device 4 is applied rotated in the direction of the arrow, and the toner T charged negatively. The toner T image is formed on the photosensitive drum 1 other than the portion irradiated with the laser light (unexposed portion). When the toner T image on the photosensitive drum 1 reaches the transfer device 5, the transfer device 5 generates a positive corona discharge, and is electrostatically transferred onto the recording paper P. A neutralization device 6 is disposed in the vicinity of the downstream of the transfer device 5. The neutralization device 6 is configured such that when the recording paper P is positively charged by the transfer of the toner T image, the recording paper P is weakly positively charged. In particular, it is intended to prevent the recording sheet P from being attracted to the photosensitive drum 1 by being attracted to the non-image area + 50V), and the charge of the recording paper P is removed by AC corona discharge on which a negative DC voltage is superimposed.

  Accordingly, the recording paper P to which the toner T image has been transferred is neutralized by passing through the neutralization device 6, separated from the photosensitive drum 1, and the recording paper P carrying the toner T image is then conveyed to the fixing device 8. Is done. The recording paper carrying the toner T image receives heat and pressure when passing through the fixing device 8, and the toner T image is fixed on the recording paper P.

  On the other hand, the photosensitive drum 1 that has completed the transfer process, after the transfer residual toner on the photosensitive drum 1 is removed by the cleaning device 7, is uniformly charged again by the charging device 2 to prepare for the next image formation.

  As described above, this embodiment is a normal development system in which the recording paper P is positively charged by the transfer device 5 and the non-image portion (exposure portion charging potential: +50 V) on the photosensitive drum 1 is weakly positive. Compared with a reversal development system in which the recording paper P of Example 1 is negatively charged by the transfer device 5 and the non-image portion (non-exposed portion charging potential: +400 V) on the photosensitive drum 1 is positive, the electrostatic adsorption force is higher. Due to the small size, the separation failure between the photosensitive drum 1 and the recording paper P hardly occurs. However, even in the regular development system, a separation failure between the photosensitive drum 1 and the recording paper P occurs in a high-speed machine.

  Therefore, in this embodiment as well, as in the first embodiment, a minute dot toner image forming method for forming a minute dot toner image on a non-image portion (white background portion) to prevent separation failure will be described.

  In the reversal development system of Example 1, a portion corresponding to a minute dot toner image in a non-image portion on the photosensitive drum 1 is exposed, and toner T is attached to the exposed portion to form minute dots. However, in the regular development system of this embodiment, the portion corresponding to the minute dot toner image in the non-image portion on the photosensitive drum 1 is not exposed, and the toner T is attached to the non-exposed portion to form a minute dot toner image.

  The fine dot toner image forming method is the same as that of the first embodiment described with reference to FIGS.

  However, in this embodiment, the separation between the photosensitive drum 1 and the recording paper P is slightly improved as compared with the first embodiment because of normal development. The fog amount of the regular development system of this embodiment may be about 1.5%, while the fog amount of the reversal development system is about 2%.

  Therefore, in this embodiment, for example, when the installation environment of the image forming apparatus is a normal environment (temperature: 23 ° C., relative humidity: 50%), as shown in the example of FIG. In the case of 1%, a fog amount of about 1.5% is used in a 0.5 to 1 dot system with a frequency of 25%.

  For example, when the installation environment of the same image forming apparatus is a high-temperature and high-humidity environment (temperature: 30 ° C., relative humidity: 70%), as shown in the example of FIG. % And the fog amount is smaller than the normal environment, a fog amount of about 1.5% is used in a one-dot system with a frequency of 50%. As described above, even when the amount of fog that can prevent separation failure varies depending on the configuration of the image forming apparatus, it is possible to easily cope with the selection of the fine dot toner image forming method (method of arbitrarily selecting the frequency and the dot system). Can do.

  As described above, also in the regular development system of this embodiment, by applying the present invention, the recording paper P corresponding to the recording paper P on the surface of the photosensitive drum 1 is applied as in the reverse development system of the first embodiment. The non-image portion (white background other than the toner T image) is irradiated with laser light so as to form a fine dot toner image different from the image information, and the fine dot toner image is developed by the developing device 4. A fine dot toner image is attached. This fine dot toner image is interposed as spacer particles between the recording paper P and the photosensitive drum 1, weakens the electrostatic adsorption force between the recording paper P and the photosensitive drum 1, and separates the recording paper P from the photosensitive drum 1. make it easier.

  Further, the fine dot toner image is hardly noticeable visually, and is a toner image based on image information on the recording paper P, similarly to an unnecessary toner called fog that adheres to a non-image portion on the recording paper P. It is possible to obtain a clear image that does not affect the (original image) and that does not cause moire or the like.

  A third embodiment according to the present invention will be described with reference to FIGS.

  FIG. 20 is an example of a color image forming apparatus 102 that uses an intermediate transfer member of a reversal development system (IAE: Image Area Exposure) for explaining Example 3 of the present invention.

  In the first and second embodiments, the black-and-white image forming apparatus has been mainly described. However, in the present embodiment, the present invention is applied to a color image forming apparatus using an intermediate transfer body, whereby the intermediate transfer body and the recording are recorded. A fine dot toner image forming method for preventing poor separation from paper will be described.

  FIG. 20 shows an example of a color image forming apparatus 102 of a tandem type intermediate transfer system.

  A color image forming apparatus 102 shown in FIG. 20 includes four image forming units, Y (yellow), M (magenta), C (cyan), and Bk (black), which form toner images of four different colors. An intermediate transfer belt 19 as an intermediate transfer member is arranged so as to pass through these image forming units.

  These four image forming units have the same configuration, and the configuration of a Y (yellow) image forming unit will be described below as a representative.

  As an image carrier, for example, a cylindrical electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 11Y whose surface layer is made of OPC (organic optical semiconductor) is driven to rotate in the direction of arrow A. Reference numeral 15Y denotes a charging roller for uniformly and uniformly charging the surface of the photosensitive drum 11Y. The charging roller 15Y to which a predetermined bias is applied rotates in contact with the photosensitive drum 11Y so that the surface of the photosensitive drum 11Y has a predetermined potential ( For example, it is charged to a charged portion potential: −400 V). The charged photosensitive drum 11Y is exposed to exposure light (laser light or the like) by the exposure device 16Y to form an electrostatic latent image (for example, exposure portion potential: −50 V) corresponding to the color separation image of the input document. Is done. The developing device 12Y is a developing roller (DC: -250V, AC: 1800Vpp) to which a bias is applied, and develops using a negatively charged toner mixed with a carrier (not shown) to cope with an electrostatic latent image. The toner image thus formed is formed on the surface of the photosensitive drum 11Y. The toner image on the photosensitive drum 11Y is primary-transferred by a primary transfer roller 13Y to which a predetermined plus bias is applied onto an intermediate transfer belt 19 as an intermediate transfer member rotating at substantially the same speed as the photosensitive drum 11Y. .

  The intermediate transfer belt 19 is stretched around a drive roller 20, a support roller 21, and a backup roller 22, and is rotationally driven in the direction of arrow B of the drive roller 20 while being in contact with the photosensitive drums 11Y, 11M, 11C, and 11Bk. The intermediate transfer belt 19 is sandwiched between the primary transfer rollers 13Y, 13M, 13C, and 13Bk and the photosensitive drums 11Y, 11M, 11C, and 11Bk, whereby the photosensitive drums 11Y, 11M, 11C, and 11Bk and the intermediate transfer belt are interposed. A primary transfer nip portion (primary transfer portion) is formed between

  The above operation is performed by the image forming unit, and the toner images formed on the photosensitive drums 11Y, 11M, 11C, and 11Bk are sequentially multiplex-transferred onto the intermediate transfer belt 19. In the full color mode, each color toner image is primarily transferred onto the intermediate transfer belt 19 in the order of Y, M, C, and Bk (the color order is arbitrary depending on the image forming apparatus). In this case, the necessary color toner is multiplex-transferred onto the intermediate transfer belt 19 in the same process as described above.

  Then, the multiple transferred toner images are recorded by the secondary transfer roller 23 to which the transfer material P taken out from the cassette 25 is supplied by the registration roller pair 24 at a predetermined timing and to which a predetermined plus bias is applied. Secondary transfer is performed on the paper P. The positively charged recording paper P is neutralized by the neutralizing needle 26 to which a negative bias is applied to separate the intermediate transfer belt 19 and the recording paper P, and the recording paper P on which the toner image is secondarily transferred is The toner image is conveyed along a conveyance path indicated by a broken line D and conveyed to the fixing device 40. The toner image on the recording paper P is pressurized and heated by the fixing device 40, and the toner image is fixed on the recording paper P.

  On the other hand, the primary transfer residual toner on the photosensitive drum 11Y after the primary transfer of the toner image is collected by the photosensitive drum cleaning device 14Y provided with a blade or a brush, and the primary transfer residual toner is removed. 11Y is again charged uniformly and uniformly by the charging roller 15Y to prepare for the next image formation. The same applies to the other image forming units.

  Further, the secondary transfer residual toner on the intermediate transfer belt 19 after the secondary transfer of the toner image is collected by the intermediate transfer belt cleaning device 30 provided with a blade or a brush, and the secondary transfer residual toner is removed. The intermediate transfer belt 19 is again prepared for the primary transfer for the next image formation.

  As described above, in this embodiment, the intermediate transfer belt 19 is positively charged by the primary transfer rollers 13Y, 13M, 13C, and 13Bk, and the recording paper P is strongly positively charged by the secondary transfer roller 23. In a high-speed machine, poor separation between the intermediate transfer belt 19 and the recording paper P occurs.

  Since the image forming apparatus 102 shown in FIG. 20 uses the intermediate transfer belt 19, the separation failure is slightly improved by applying curvature separation by reducing the diameter of the backup roller. In an image forming apparatus that employs (not shown), since it is difficult to reduce the diameter of the intermediate transfer drum, the separation failure is extremely severe.

  Therefore, in this embodiment as well, as in the first embodiment, a minute dot toner image is formed by forming a minute dot toner image on the non-image portion of four colors (white background portion where four colors are superimposed) to prevent separation failure. The method will be described.

  Also in this embodiment, a minute dot toner image is formed on the non-image portion of four colors corresponding to the recording paper P on at least one of the photosensitive drums 11Y, 11M, 11C, and 11Bk, and the minute dot toner image is formed. When the intermediate transfer belt 19 is primarily transferred and secondarily transferred from the intermediate transfer belt 19 to the recording paper P and separated from the intermediate transfer belt 19 and the recording paper P, a minute dot toner image is recorded on the intermediate transfer belt 19. It acts as spacer particles between the paper P and can prevent poor separation.

  As in the first embodiment described with reference to FIGS. 3 to 18, the minute dot toner image forming method selects the frequency and the dot system and sets the fog amount to about 1.5% in one unit (= 16 pixel units). In addition to preventing poor separation, other image defects such as being conspicuous visually are not generated. For example, in the case of the color image forming apparatus shown in the example of FIG. 17, a fog amount of about 1.5% is used in a 0.5 to 1 dot system with a frequency of 25%.

  In addition, since the first and second embodiments are set so as not to be visually conspicuous assuming a black and white image forming apparatus, the fine dot toner image forming method of the present embodiment is a four-color non-image. When forming a minute dot toner image on the portion, any toner color may be used, and only one arbitrary color may be formed as the minute dot toner image. A color minute dot toner image may be formed.

  In the case of the present embodiment, it is not necessary to limit the minute dot toner image to yellow dots in particular. Therefore, the photosensitive drums 11Y, 11M, and 11C are detached from the intermediate transfer belt 19 when the black monochrome image is formed. The image forming apparatus of the type that extends the life of the photosensitive drum because the contact belt and the transfer belt are not in contact with each other has an advantage that fine dots need only be formed in black.

  As described above, also in the color image forming apparatus of this embodiment, by applying the present invention, the recording paper P corresponding to the recording paper P on the surface of the photosensitive drum is applied as in the first and second embodiments. The four-color non-image part is irradiated with laser light so as to form a fine dot toner image different from the image information, and the fine dot toner image is developed by a developing device to attach the fine dot toner image. A fine dot toner image is transferred from the photosensitive drum to the intermediate transfer belt 19 by primary transfer, and the fine dot toner image is interposed as a spacer particle between the recording paper P and the intermediate transfer belt 19, and The electrostatic attracting force between the transfer belts 19 is weakened, and the separation of the recording paper P from the intermediate transfer belt 19 is facilitated.

  Further, the fine dot toner image is hardly noticeable visually and is based on the image information on the recording paper P, like the unnecessary toner called fog that adheres to the non-image portions of the four colors on the recording paper P. In addition, a clear color image that does not affect the toner image (original image) and does not generate moire or the like can be obtained.

  Although the embodiments of the present invention have been described above, the numerical values such as the number of pixels of one unit, the minute dot formation pattern, the frequency, and the dot system in the embodiments 1 to 3 of the present invention are simplified. The numerical values can be arbitrarily determined according to the configuration and settings of the image forming apparatus.

  Further, the present invention is not limited to the image forming apparatus described in the embodiments, and can be applied to other forms of image forming apparatuses such as any combination of the embodiments.

1 is a schematic cross-sectional view illustrating an example of a reversal development type image forming apparatus 100 according to Embodiment 1 of the present invention. It is explanatory drawing of the conventional fogging amount adjustment method. FIG. 3 is a schematic diagram illustrating an example of one unit for forming a fine dot toner image according to an embodiment of the present invention. It is a schematic diagram showing an example of a minute dot toner image formation pattern that can be visually recognized as a dot of the minute dot toner image according to the embodiment of the present invention. It is a schematic diagram which shows another example of the fine dot toner image formation pattern which can be recognized visually as the dot of the fine dot toner image which concerns on the Example of this invention. FIG. 4 is a schematic diagram illustrating an example of a minute dot toner image formation pattern that cannot be visually recognized as a dot of a minute dot toner image according to an embodiment of the present invention. It is a schematic diagram which shows another example of the fine dot toner image formation pattern which cannot be recognized visually as the dot of the fine dot toner image which concerns on the Example of this invention. FIG. 6 is a schematic diagram illustrating an example of a fine dot toner image formation pattern for explaining a problem related to a combination of a plurality of fine dot toner images according to an embodiment of the present invention. FIG. 6 is a schematic diagram illustrating an example of a minute dot toner image formation pattern for explaining a problem that a minute dot toner image and an original image are adjacent to each other according to an embodiment of the present invention. FIG. 5 is a schematic diagram illustrating an example of a 0.5 dot (0.5 pixel) micro dot toner image formation pattern according to an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an example of a 1-dot (1-pixel) micro dot toner image formation pattern according to an embodiment of the present invention. FIG. 4 is a schematic diagram illustrating an example of a 1.5 dot (1.5 pixel) micro dot toner image formation pattern according to an embodiment of the present invention. FIG. 4 is a schematic diagram illustrating an example of a 1.5 dot (1.5 pixel) micro dot toner image formation pattern according to an embodiment of the present invention. FIG. 4 is a schematic diagram illustrating an example of a 2-dot (2-pixel) micro dot toner image formation pattern according to an embodiment of the present invention. FIG. 4 is a schematic diagram illustrating an example of a 0.5 to 1 dot (0.5 to 1 pixel) micro dot toner image formation pattern according to an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an example of a 1 to 1.5 dot (1 to 1.5 pixel) micro dot toner image formation pattern according to an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an example of a 1.5 to 2 dot (1.5 to 2 pixel) micro dot toner image formation pattern according to an embodiment of the present invention. It is explanatory drawing which shows an example of fog amount adjustment (dot system and frequency) which concerns on the Example of this invention. It is explanatory drawing which shows another example of fog amount adjustment (dot system and frequency) which concerns on the Example of this invention. FIG. 6 is a schematic cross-sectional view illustrating an example of a regular development type image forming apparatus 101 according to a second embodiment of the present invention. FIG. 6 is a schematic cross-sectional view illustrating an example of a color image forming apparatus 102 of a reversal development system according to Embodiment 3 of the present invention.

Explanation of symbols

1, 11Y, 11M, 11C, 11Bk photoconductor (photosensitive drum)
2, 15Y, 15M, 15C, 15Bk Charging device 3, 16Y, 16M, 16C, 16Bk Exposure device 4, 12Y, 12M, 12C, 12Bk Developing device 5 Transfer device 6, 26 Static eliminating device 8, 40 Fixing device 13Y, 13M, 13C, 13Bk Primary transfer roller 23 Secondary transfer roller 100 Reverse development system image forming apparatus 101 Regular development system image forming apparatus 102 Color image forming apparatus M using reverse development system intermediate transfer body Toner image based on image information ( The original image)
P Recording material T Toner

Claims (8)

The photosensitive member is charged by a charging device, the photosensitive member is exposed to light based on image information by an exposure device, an electrostatic latent image is formed on the surface of the photosensitive member, and the electrostatic latent image is developed by a developing device. A toner image as image information is formed on the surface of the photosensitive member, and the toner image is transferred to a recording sheet by a transfer device, or the toner image is transferred to an intermediate transfer member by a primary transfer device, and then on the intermediate transfer member. In the image forming apparatus for transferring the toner image to the recording paper by the secondary transfer device, transporting the recording paper carrying the toner image to the fixing device, and fixing the toner image on the recording paper.
A fine dot toner image is formed on a non-image portion (white background portion) other than the toner image portion as image information on the recording paper, and the fine dot toner image is not formed adjacent to the toner image as image information. In addition, the image forming apparatus controls the formation position of the minute dot toner image according to the toner image position as the image information. The photosensitive member is charged by a charging device, the photosensitive member is exposed to light based on image information by an exposure device, an electrostatic latent image is formed on the surface of the photosensitive member, and the electrostatic latent image is developed by a developing device. A toner image as image information is formed on the surface of the photosensitive member, and the toner image is transferred to a recording sheet by a transfer device, or the toner image is transferred to an intermediate transfer member by a primary transfer device, and then on the intermediate transfer member. In the image forming apparatus for transferring the toner image to the recording paper by the secondary transfer device, transporting the recording paper carrying the toner image to the fixing device, and fixing the toner image on the recording paper.
A fine dot toner image is formed on a non-image portion (white background portion) other than the toner image portion as image information on the recording paper. The fine dot toner image has a predetermined unit of a plurality of pixels as one unit. An image forming apparatus, wherein the image forming apparatus is formed at a central pixel position excluding an outer peripheral portion equal to or more than a minimum pixel. 2. The size (number of dots forming pixels) of a minute dot toner image formed on the non-image portion is 1200 dpi 2.25 dots (2.25 pixels) or less, that is, 1100 μm ² or less. Alternatively, the image forming apparatus according to claim 2.   The minute dot toner image formation position is determined by selecting a dot formation pattern for each unit by random numbers from a plurality of different dot formation patterns corresponding to a predetermined number of dot formation pixels at the dot formation pixel position in the one unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is determined.   For fine dot toner image formation, “dot formation” and “dot formation” are selected for each unit with random numbers based on a predetermined frequency (0 to 100%) at the dot formation pixel position in one unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is determined by performing the operation.   For fine dot toner image formation, “dot formation” and “dot formation” are selected for each unit with random numbers based on a predetermined frequency (0 to 100%) at the dot formation pixel position in one unit. The dot formation pattern is determined by selecting a dot formation pattern for each unit for dot formation from a plurality of different dot formation patterns corresponding to the number of dot formation pixels of one unit by random numbers. Item 4. The image forming apparatus according to any one of Items 3.   7. The image forming apparatus according to claim 6, wherein the number of fine dot toner images in the non-image area on the recording paper is determined by a combination of the number of dots formed by one unit and the frequency (0 to 100%). .   According to the image forming mode, the type of recording paper, or the environment, the number of dot forming pixels of one unit of the minute dot toner image formed on the non-image portion and the frequency (0 to 100%) are variable. The image forming apparatus according to claim 7.

Images