JP5217548B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a color copying machine or a color printer to which an electrophotographic system is applied.

JP-A-4-362960 JP 11-202583 A JP 2007-108585 A JP 2004-135317 A

  In recent years, image forming apparatuses such as color copiers and color printers to which this type of electrophotographic system is applied have been required to have higher image quality, which is close to photographic images when forming full-color images. It is required to form an image having glossiness. For this reason, the image forming apparatus is configured to form an image using a transparent toner in order to give gloss in addition to color toners such as yellow, magenta, and cyan.

  As a technique relating to such an image forming apparatus, for example, those disclosed in JP-A-4-362960, JP-A-11-202583, JP-A-2007-108585, JP-A-2004-135317, and the like. Various proposals have already been made.

  By the way, the color image forming method according to the above-mentioned JP-A-4-362960 is configured such that the color toner image formed on the transfer material is composed of a fixed color toner adhesion area and a transparent toner adhesion area. Is.

  Further, the image forming method according to the above-mentioned Japanese Patent Application Laid-Open No. 11-202583 includes a step of forming an electrostatic latent image having a line structure on an image carrier, and the electrostatic latent image is colored using colored toner and transparent toner. An image forming method comprising a step of developing and a step of transferring a formed developed image to a transfer body, wherein an image signal of a colored toner is formed in the step of forming an electrostatic latent image having a line structure on the image carrier. By modulating the image signal of the transparent toner based on the above, ON / OFF of the laser beam for exposure is controlled, and the transparent toner is developed between the lines of the colored toner.

Further, the image processing apparatus according to the above Japanese Patent Application Laid-Open No. 2007-108585 is an image processing apparatus that converts multi-gradation image data into halftone image data having a predetermined number of gradations,
Input means for inputting first multi-tone image data that is a source of image formation with specific colored toner and second multi-tone image data that is a source of image formation with transparent toner;
The first multi-tone image data is converted by a dither method using a first dot-concentrated dither matrix, and the second multi-tone image data is dithered using a second dot-concentrated dither matrix. Conversion means for converting by
Output means for outputting first halftone image data that is the conversion result of the first multi-tone image data and second halftone image data that is the conversion result of the second multi-tone image data Are provided.

  In addition, the color image processing apparatus according to Japanese Patent Application Laid-Open No. 2004-135317 performs FM screen processing in a color image processing apparatus that performs halftone processing for each color component on a color image signal composed of a plurality of color components. FM screen processing means is provided, and the FM screen processing means performs FM screen processing on at least one color component of the color image signal.

  Generally, the number of screen lines used in the image forming apparatus is set to about 150 to 300 lines in order to stabilize the structure of the toner formed on the photosensitive drum. Further, in Patent Document 3, in order to reduce the consumption of transparent toner, the amount of transparent toner is controlled according to the amount of chromatic color toner, or the screen line number of transparent toner is made higher than that of chromatic color toner. A technique for forming an image has been proposed.

  However, in the case of the above-described conventional image forming apparatus, the number of screen lines of the transparent toner is set to about 300 lines, and in order to reduce the consumption of the transparent toner, the transparent toner is changed according to the amount of chromatic toner. When the amount is regulated, as shown in FIG. 15, the difference in glossiness generated between the gloss of the transparent toner portion and the gloss of the chromatic color toner portion becomes large, resulting in uneven gloss, or as shown in FIG. Since the toner layer becomes higher at the place where the screen structure of the transparent toner and the screen structure of the chromatic color toner overlap, the toner scattering is likely to occur at the time of transfer to the paper, and the toner scattering corresponds to the screen structure. Therefore, it has a technical problem that a moire pattern is generated due to periodic generation.

  By the way, the problem to be solved by the present invention is that uneven gloss caused by the difference between the gloss of the transparent toner portion and the glossy of the chromatic color toner portion, or the toner scattering periodically occurs at the position where the transparent toner and the chromatic color toner overlap. An object of the present invention is to provide an image forming apparatus capable of suppressing moire patterns resulting from the above.

That is, the invention described in claim 1 includes an image forming unit that forms an image made of at least one chromatic toner and an image made of a transparent toner;
Transfer means for transferring an image made of at least one chromatic toner formed by the image forming means and an image made of transparent toner onto a recording medium so that the image made of transparent toner is positioned on the uppermost layer;
When forming an image by the image forming means, a first mode in which a transparent toner is used to form an image on the recording medium having an uneven surface, and a transparent toner is used to reduce a gloss difference in the image. Mode setting means for setting a plurality of different modes including the second mode to be used ;
According to the mode set by the mode setting means, the maximum density image area ratio when forming the image made of the transparent toner is changed so that the second mode is lower than the first mode. And an image forming condition changing unit.

Further, the invention described in claim 2 converts multi-tone image data corresponding to at least one chromatic color into halftone image data having a predetermined number of gradations using a screen, and is transparent. Data conversion means for converting the corresponding multi-gradation image data into halftone image data having a predetermined gradation number using a screen having a larger number of screen lines than the chromatic toner screen;
Image forming means for forming an image made of at least one chromatic toner and an image made of transparent toner based on halftone image data corresponding to at least one chromatic color and transparency converted by the data conversion means; ,
Transfer means for transferring an image made of at least one chromatic toner formed by the image forming means and an image made of transparent toner onto a recording medium so that the image made of transparent toner is positioned on the uppermost layer;
When forming an image by the image forming means, a first mode in which a transparent toner is used to form an image on the recording medium having an uneven surface, and a transparent toner is used to reduce a gloss difference in the image. Mode setting means for setting a plurality of different modes including the second mode to be used;
In accordance with the mode set by the mode setting means, the image area ratio of the maximum density when forming an image made of the transparent toner is changed so that the second mode is lower than the first mode. And an image forming condition changing unit .

  Furthermore, the invention described in claim 3 is the image forming apparatus according to claim 1 or 2, wherein the image forming apparatus performs laser exposure on the photosensitive member of the image forming unit to form an electrostatic latent image. In the image forming apparatus, the number of screen lines is set to decrease as the beam diameter of the laser beam increases.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, a screen line of laser light for forming an electrostatic latent image by performing image exposure on the photosensitive member of the image forming means. An image forming apparatus characterized by satisfying a relationship of L ≧ −1.4R + 391 where L is the number and R is the beam diameter of the laser light.

  Further, in the invention described in claim 5, in the image forming apparatus according to any one of claims 1 to 4, the number of screen lines when forming the image of the transparent toner is set to 340 lines or more. An image forming apparatus characterized by the above.

  According to the first aspect of the present invention, gloss unevenness caused by the difference between the gloss of the transparent toner portion and the gloss of the chromatic color toner portion, or the toner scattering periodically occurs at a position where the transparent toner and the chromatic color toner overlap. It is possible to suppress the moire pattern resulting from the operation.

According to the first and second aspects of the present invention, by changing the image area ratio of the maximum density when forming an image made of transparent toner in a mode in which uneven glossiness and moire patterns tend to appear remarkably. To suppress gloss unevenness caused by the difference between the gloss of the transparent toner portion and the glossy of the chromatic color toner portion, and moire patterns caused by the periodic occurrence of toner scattering at the position where the transparent toner and the chromatic color toner overlap. Is possible.

  Further, according to the third aspect of the present invention, it is possible to effectively suppress the moire pattern even when the beam diameter of the laser beam varies due to component errors or the like.

  According to the fourth aspect of the present invention, it is possible to reliably suppress the moire pattern even when the beam diameter of the laser beam varies due to component errors or the like.

  Furthermore, according to the fifth aspect of the present invention, even when the beam diameter of the laser light varies due to component errors or the like, it is possible to reliably suppress the moire pattern.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1
FIG. 2 shows a tandem digital color printer as an image forming apparatus according to Embodiment 1 of the present invention. Of course, the image forming apparatus may be a multifunction machine having functions such as a printer, a copying machine, and a facsimile machine.

  In FIG. 2, reference numeral 1 denotes a main body of a tandem type digital color printer. Inside the color printer main body 1, as an image corresponding to at least one chromatic color and transparency, transparent (CT), yellow Five image forming units 2CT, 2Y, 2M, 2C, and 2K that form images of each color of (Y), magenta (M), cyan (C), and black (K) are spaced apart in the horizontal direction. They are arranged in parallel. Further, inside the color printer main body 1 is provided an image processing apparatus 3 that performs predetermined image processing on image data output from a personal computer, a scanner, or the like (not shown).

  The five image forming units 2CT, 2Y, 2M, 2C, and 2K are configured in the same manner except for the color of the image to be formed. As shown in FIG. The photosensitive drum 4 as an image carrier that is rotationally driven by the arrow A direction, the charging roll 5 for primary charging that uniformly charges the surface of the photosensitive drum 4, and the photosensitive drum 4 An image exposure device 6 that forms an electrostatic latent image by exposing an image corresponding to a predetermined color on the surface, and a developing unit that develops the electrostatic latent image formed on the photosensitive drum 4 with toner of a predetermined color 7, a cleaning device 8 that cleans the surface of the photosensitive drum 4, and an erase lamp 9 that erases the electrostatic latent image remaining on the photosensitive drum 4.

  In addition, as the charging roll 5, for example, a roll-shaped charger in which a conductive layer made of synthetic resin or rubber and having an adjusted electric resistance is coated on the surface of the core metal is used. A predetermined AC bias voltage or an AC bias voltage superimposed with a DC bias voltage is applied.

  Further, as shown in FIG. 2, the image exposure apparatus 6 is configured to correspond to five image forming units 2CT, 2Y, 2M, 2C, and 2K, and uses five semiconductor lasers (not shown) for each color of image data. Are modulated according to the above, and the five laser beams LB-CT, LB-Y, LB-M, LB-C, and LB-K are emitted from these semiconductor lasers. Of course, the image exposure device 8 may be individually configured for each of a plurality of image forming units. The laser beams LB-CT, LB-Y, LB-M, LB-C, and LB-K are scanned and exposed obliquely from below onto the photosensitive drum 4 through a rotating polygon mirror and a plurality of reflecting mirrors (not shown). Is done.

  Further, the image processing apparatus 3 converts the image forming units 2CY, 2Y, 2M, 2C, and 2K for each color of transparent (CT), yellow (Y), magenta (M), cyan (C), and black (K). Image data of each color is sequentially output to the corresponding image exposure apparatus 6, and laser beams LB-CT, LB-Y, LB-M, and LB emitted according to the image data from the image exposure apparatus 6. -C and LB-K are subjected to scanning exposure on the surface of the corresponding photosensitive drum 4 to form an electrostatic latent image. The electrostatic latent images formed on the photosensitive drum 4 are respectively transparent (CT), yellow (Y), magenta (M), cyan (C), and developing units 7CT, 7Y, 7M, 7C, and 7K. It is developed as a toner image of each color of black (K).

  Transparent (CT), yellow (Y), magenta (M), cyan (C), and black (black) (sequentially formed on the photosensitive drums 4 of the image forming units 2CT, 2CT, 2Y, 2M, 2C, and 2K. The color toner images K) are transferred in multiple by the primary transfer roll 11 onto the intermediate transfer belt 10 disposed over the image forming units 2CT, 2Y, 2M, 2C, and 2K. The intermediate transfer belt 10 is wound around the drive roll 12, the backup roll 13, the tension roll 14, and the idler roll 15 with a constant tension, and has excellent constant speed properties as will be described later. The drive roll 12 is rotationally driven by a dedicated drive motor and is circulated and driven in the direction of arrow B at a predetermined moving speed. As the intermediate transfer belt 10, for example, a flexible synthetic resin film such as polyimide is formed in a band shape, and both ends of the synthetic resin film formed in a band shape are connected by means such as welding, thereby being endless. A belt-shaped one is used.

  Transparent (CT), yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred multiple times on the intermediate transfer belt 10 with the transparent (CT) toner as the lowest layer The recording paper 17 is secondarily transferred onto a recording paper 17 as a recording medium by a secondary transfer roll 16 that is in pressure contact with the backup roll 13 via the intermediate transfer belt 10, and the toner image of each color is transferred onto the recording paper 17. Then, it is conveyed along the one side wall of the printer main body 1 to the fixing device 18 positioned above. The secondary transfer roll 16 is in pressure contact with the side of the backup roll 13 and secondarily transfers the toner images of the respective colors onto the recording paper 17 conveyed along the upper side from the lower side in the vertical direction. ing. The recording paper 17 on which the toner images of the respective colors are transferred is subjected to a fixing process by heat and pressure by a fixing unit 18 and then discharged from a discharge port 20 to an upper portion of the printer main body 1 by a discharge roll 19. 21 is discharged.

  As shown in FIG. 2, the recording paper 17 is of a predetermined size and material from the storage tray 22 via a paper transport path 25 and a transport roll 26 by a feed roll 23 and a roll pair 24 for paper separation and transport. After being conveyed to the registration roll 27, it is stopped. The recording paper 17 supplied from the storage tray 22 is sent to the secondary transfer position of the intermediate transfer belt 10 by a registration roll 27 that rotates at a predetermined timing.

  As the recording paper 17, in addition to plain paper, coated paper in which a coating layer is formed on one or both sides of the paper, embossed paper, or the like is used.

  In FIG. 2, 28 and 29 are paper detection sensors and paper thickness detection sensors provided in the paper conveyance path 25, and 30CT, 30Y, 30M, 30C and 30K are transparent (CT), yellow (Y), A toner cartridge that supplies toner of a predetermined color to the developing devices 7 of magenta (M), cyan (C), and black (K), and 31 a cleaning device that cleans the surface of the intermediate transfer belt 10. ing.

  FIG. 3 shows each image forming unit of the digital color printer.

  The five image forming units 2CT, 2Y, 2M, 2C, and 2K of transparent, yellow, magenta, cyan, and black are all configured similarly as shown in FIG. In the image forming units 2CT, 2Y, 2M, 2C, and 2K, as described above, transparent, yellow, magenta, cyan, and black toner images are sequentially formed at predetermined timings, respectively. . As described above, the image forming units 2CT, 2Y, 2M, 2C, and 2K for the respective colors are provided with the photosensitive drums 4, and the surfaces of these photosensitive drums 4 are covered with a charging roll 5 for primary charging. It is charged like this. Thereafter, the surface of the photosensitive drum 4 is scanned and exposed to an image forming laser beam LB emitted from the image exposure device 6 according to the image data, and an electrostatic latent image corresponding to each color is formed. The laser beam LB scanned and exposed on the photosensitive drum 4 is set so as to be exposed at a predetermined inclination angle from an obliquely lower side slightly to the right of the photosensitive drum 4. The electrostatic latent image formed on the photosensitive drum 4 is transparent, yellow, magenta, cyan, by the developing roll 7a of the developing unit 7 of each image forming unit 2CT, 2Y, 2M, 2C, and 2K. Each of the black toners is developed into a visible toner image, and these visible toner images are sequentially transferred onto the intermediate transfer belt 10 in multiple layers by the charging of the primary transfer roll 11.

  Each of the developing devices 7CT, 7Y, 7M, 7C, and 7K adopts a two-component developing method using a two-component developer composed of toner and carrier, and the surface of the developing roll 7a is composed of toner and carrier. A magnetic brush of component developer is formed to develop the electrostatic latent images formed on the surfaces of the corresponding color photosensitive drums 4CT, 4Y, 4M, 4C, and 4K. As the developer, a one-component developer composed only of toner may be used.

  The surface of the photoconductive drum 4 after the toner image transfer process is finished, the residual toner, paper dust, and the like are removed by the cleaning device 9 and the exposure is performed uniformly by the erase lamp 9 and the remaining static is left. The electrostatic latent image is erased and prepared for the next image forming process. The cleaning device 8 includes a cleaning blade and a cleaning brush, and residual toner on the photosensitive drum 4 is removed by the cleaning blade and the brush.

  Further, as shown in FIG. 2, the toner remaining on the surface of the intermediate transfer belt 10 after the toner image transfer process is removed by a cleaning device 31 to prepare for the next image forming process.

By the way, in this embodiment, multi-gradation image data corresponding to at least one chromatic color is converted into halftone image data having a predetermined number of gradations using a line screen, and also transparent. Data conversion means for converting multi-tone image data into halftone image data having a predetermined number of gradations using a line screen having a number of screen lines larger than that of the chromatic toner line;
Image forming means for forming an image made of at least one chromatic toner and an image made of transparent toner based on halftone image data corresponding to at least one chromatic color and transparency converted by the data conversion means; ,
Mode setting means for setting a plurality of different modes when forming an image by the image forming means;
Image forming condition changing means for changing an image forming condition when forming an image made of the transparent toner in accordance with the mode set by the mode setting means.

  In this embodiment, a photographic image output mode and an embossed paper output mode are provided as the plurality of different modes.

Further, in this embodiment, the image forming condition changing unit changes the image area ratio of the maximum density when forming the image made of the transparent toner according to the mode set by the mode setting unit. It is configured.

  That is, as shown in FIG. 2, the digital color printer supports at least one chromatic color sent from a personal computer (not shown), for example, four colors of yellow, magenta, cyan, and black. The image processing apparatus 3 is provided as data conversion means for converting the multi-gradation image data into binary halftone image data having a predetermined number of gradations by performing binarization processing. For example, the image processing apparatus 3 performs area gradation on a 256-gradation image data using a dither matrix and converts the image data into halftone image data having a predetermined number of gradations.

  As shown in FIG. 4, the image processing apparatus 3 includes an address generator 51, a dither matrix memory 52, and a comparator 53. The address generator 51 receives pixel position information indicating the position of each pixel in the image data and matrix information indicating the size and angle of the dither matrix defined for each color of the image data. The address generator 51 uses the pixel position information indicating the position of each pixel in the image data and the matrix information indicating the size and angle of the dither matrix defined for each color of the image data in the corresponding dither matrix. Address information indicating the corresponding position of each pixel is generated.

  The dither matrix memory 52 stores a dither matrix in which threshold information corresponding to all positions in the image data is stored. The dither matrix memory 52 receives address information from the address generator 51 and outputs threshold information at a position in the dither matrix corresponding to the address information.

  Further, the comparator 53 compares the threshold information output from the dither matrix memory 52 with the corresponding multi-gradation (for example, 256 gradations) image data, and compares the comparison result with a predetermined number of gradations. This is output as halftone image data. The comparator 53 includes input means for inputting multi-gradation image data, conversion means for converting the image data into halftone image data having a predetermined number of gradations, and output means for outputting the conversion result. It is out.

  In this embodiment, a dither matrix having a resolution of 1200 dpi is stored in the dither matrix memory 52. Specifically, in the dither matrix memory 52, as shown in FIG. 5, a dither matrix composed of a basic dither matrix having a line screen angle of 0 degrees and a screen line number of 240 lines is used for yellow. As shown in FIG. 6, a dither matrix composed of a basic dither matrix having a line screen angle of 26.5 degrees and a screen line number of 240 lines is used for magenta, and as shown in FIG. A dither matrix composed of a basic dither matrix having an angle of 64.6 degrees and 240 lines is used for cyan, and a dither matrix comprising a basic dither matrix having a screen angle of 0 degrees and a screen line number of 400 lines as shown in FIG. Is stored for transparent toner.

  The dither matrix for black color is the same as that for yellow shown in FIG. 5, for example, except that the basic line dither matrix has a line screen angle of 90 degrees and a screen line number of 240 lines. A dither matrix is used.

  As described above, the number of screen lines of the transparent toner line screen is set to be larger than that of the chromatic toner line screens for yellow, magenta, and cyan.

  Further, regarding the color toner, in order to increase the number of gradations, 8 to 16 basic dither matrices may be combined to ensure a sufficient number of gradations. In this embodiment, since the basic dither matrix as shown in FIG. 8 is used for the transparent toner, the number of screen lines for the transparent toner is 1200/3 = 400 lines per inch. That is, since the screen line interval is 254 (mm) /400=63.5 μm, it is almost the same as the beam diameter of laser exposure and is hardly resolved. With transparent toner, the dither matrix is smaller than the color toner as described above, but the tonality is impaired. However, since the transparent toner is difficult to be visually recognized, there is no such problem, and the dither matrix can be stored. An effect is obtained that the amount of memory of the necessary dither matrix memory 52 can be reduced.

  The “transparent toner” does not mean only a completely transparent toner that does not absorb visible light at all, but is used as a concept including a toner that slightly absorbs visible light. “Color toner” is synonymous with toner having color (chromatic toner), but this chromatic toner does not exclude black, white and other achromatic colors, and toner other than “transparent toner”. It means the whole thing.

  In the image processing apparatus 3 configured as described above, image data output to the image exposure apparatus 6 is generated as follows based on each dither matrix stored in the dither matrix memory 52.

  In the image processing device 3, as shown in FIG. 4, first, pixel position information for the pixel of interest in the image data, and matrix information indicating the size and angle of the dither matrix defined for each color of the image data, Is input to the address generator 51. The address generator 51 generates address information indicating the position corresponding to the pixel position information in the dither matrix for each color.

  For example, for the dither matrix for transparent toner shown in FIG. 8, information “3 rows, 3 columns, 0 °” is input to the address generator 51 as matrix information. As the pixel position information, if the pixel position is expressed in the form of (row number, column number), (1, 1), (1, 2), ..., (2, 1), (2 , 2),..., (3, 1), (3, 2),. Thereby, address information indicating which position in the dither matrix specified by each piece of pixel position information is output to the dither matrix memory 52.

  As described above, when the address information output from the address generator 51 is input to the dither matrix memory 52, threshold information is output from the dither matrix memory 52.

  For example, in the dither matrix for transparent toner shown in FIG. 8, if the position in the dither matrix is expressed in the form of (row number, column number), the threshold information “ 2 ”, threshold information“ 5 ”is output for the address information (1, 2), and threshold information“ 7 ”is output for the address information (1, 3).

  Also, threshold information “6” for address information (2,1), threshold information “1” for address information (2,2), and threshold information “4” for address information (2,3). ”Is threshold information“ 8 ”for the address information (3,1), threshold information“ 2 ”is for the address information (3,2), and threshold information“ 3 ”is for the address information (3,3). 3 "is output.

  The threshold information output from the dither matrix memory 52 in this way is input to the comparator 53. Further, multi-gradation image data is input to the other side of the comparator 53.

  In the multi-gradation image data, yellow, magenta, and cyan are represented by 256 gradations from 0 to 255, for example. On the other hand, for transparent toner, an image signal for transparent toner obtained as follows is input as image data. That is, the total value is calculated for the three-color color toner multi-value input signal, and as shown in FIG. 9, if the total value is 140% or less, the transparent toner image signal is set to 100%, If it exceeds 240%, the image signal for transparent toner is set to 0%. When the total value is 140% or more and 240% or less, the image signal for transparent toner is obtained by linearly decreasing from 100% to 0%. According to such a method, when an average color image is input, it is possible to reduce the consumption amount of the transparent toner to about a half as compared with the case where the transparent toner is uniformly attached to the entire surface 100%.

  The comparator 53 compares the multi-tone image data with the threshold information. If the image data is equal to or greater than the threshold, the comparator 53 outputs “1” as the comparison result. If the image data is less than the threshold, the comparison is performed. As a result, “0” is output. This is performed for each color component for all pixels in the image data.

  For example, if the transparent toner image signal is 0%, the image data is 0, so that the comparison result “0” is output for all positions in the dither matrix. As a result, the output result is as shown in FIG.

  If the transparent toner image signal is 30%, the image data is 2.7 (= 9 × 30%). Therefore, the positions corresponding to the dither matrix thresholds “1” and “2” are compared. “1” is output, and the comparison result “0” is output for the positions corresponding to the threshold values “3” to “9” of the dither matrix. As a result, the output result is as shown in FIG.

  Further, assuming that the image signal for transparent toner is 50%, the image data is 4.5 (= 9 × 50%), so the positions corresponding to the dither matrix thresholds “1” to “4” are compared. The result “1” is output, and the comparison result “0” is output for the positions corresponding to the threshold values “5” to “9” of the dither matrix. As a result, the output result is as shown in FIG.

  Furthermore, if the image signal for transparent toner is 100%, the image data is 9 (= 9 × 100%), so all the positions corresponding to the threshold values “1” to “9” of the dither matrix are The comparison result “1” is output. As a result, the output result is as shown in FIG.

  Further, if the transparent toner image signal is 80%, the image data is 7.2 (= 9 × 80%), and therefore all the positions corresponding to the threshold values “1” to “9” of the dither matrix. The comparison result “1” is output. As a result, the output result is as shown in FIG.

  Further, in this embodiment, as shown in FIG. 1, a mode setting button 60 is provided as a mode setting means for setting a plurality of different modes when an image is formed by the image forming means. Here, a plurality of different modes include a photographic image output mode for outputting glossy photographic images using transparent toner, and an embossed paper output mode for outputting embossed paper that is special paper using transparent toner. And are installed. Here, the embossed paper output mode for outputting the embossed paper forms a toner image of transparent toner on the intermediate transfer belt 10 in advance, so that the color toner image can be transferred even if the surface is uneven. This is an image output mode in which the rate is 100%. In the embossed paper output mode, if the toner amount of the transparent toner is small, there is a possibility that a transfer rate of the color toner image is reduced or an image quality defect such as density unevenness occurs.

  Then, the user is configured to select and set a mode using a mode setting button 60 provided in a user interface of the printer, a driver installed in a personal computer, or the like.

  Further, in the printer, the photographic image output ROM 61 and embossed paper as image forming condition changing means for changing the image forming conditions when forming an image made of transparent toner according to the mode set by the mode setting button 60. And an output ROM 62. As shown in FIG. 1, the photographic image output ROM 61 and the embossed paper output ROM 62 have a photographic image output according to the mode set by the mode setting button 60 when the mode is set by the mode setting button 60. The output ROM 61 or the embossed paper output ROM 62 is selected, and the photographic image output ROM 61 or the embossed paper output ROM 62 is configured to change the image area ratio of the maximum density when forming an image made of transparent toner. ing.

  In this embodiment, as shown in FIG. 1, when the photographic image output mode is designated, the photographic image output ROM 61 is selected, and the image area of the maximum density is selected according to the image information of the input transparent toner image. When the embossed paper output mode is designated by changing the ratio to be set to 80%, the embossed paper output ROM 62 is selected, and the image area ratio of the maximum density is selected according to the image information of the input transparent toner image. Is set to 100% as usual. The image area ratio of the maximum density is set so that the image area ratio of the maximum density is 80% or 100% by converting the input signal into the output signal using the table set as shown in FIG. Is done. When the embossed paper output mode is designated, the input signal may be output as it is without referring to the setting table as shown in FIG.

Here, when the photographic image output mode is designated, the image area ratio of the maximum density is set to 80%, and the dither matrix shown in FIG. 10 (e) is output even when the maximum density is 100%. The toner amount (TMA) when the maximum density is 100% is limited to 3.5 g / m ² , but when the embossed paper output mode is designated, the image area ratio of the maximum density is 100. %, And the toner amount (TMA) when the maximum density is 100% is set to 4.5 g / m ² .

  In the above configuration, in the digital color printer according to this embodiment, gloss unevenness caused by the difference between the gloss of the transparent toner portion and the gloss of the chromatic color toner portion, or the transparent toner and the chromatic color toner are detected as follows. It is possible to suppress a moire pattern resulting from the periodic occurrence of toner scattering at the overlapping position.

  That is, in the digital color printer according to this embodiment, as shown in FIG. 2, the transparent, yellow, magenta, cyan, and black image forming units 2CT, 2Y, 2M, 2C, and 2K are transparent. , A toner image of a predetermined color is formed based on each image data of yellow, magenta, cyan and black, and each of these image forming units 2CT of transparent, yellow, magenta, cyan and black The transparent, yellow, magenta, cyan, and black toner images formed in 2Y, 2M, 2C, and 2K are sequentially transferred onto the intermediate transfer belt 10 in a multiplex manner, and then transferred onto the intermediate transfer belt 10. To the recording paper 17 at a time, and secondarily transferred and fixed, and a full-color image is formed.

  At this time, in the digital color printer, as shown in FIG. 2, when multi-tone image data of transparent, yellow, magenta, cyan, and black are input to the image processing device 3, the image In the processing device 3, each multi-tone image data corresponding to each color is converted into halftone image data.

  At this time, in the digital color printer, when the photographic image output mode is designated by the mode setting button 60, the image area ratio of the maximum density is referred to by referring to the photographic image output ROM 61 as shown in FIG. Is switched to 80%.

Therefore, when the photographic image mode is designated by the digital color printer, even if the image area ratio of the maximum density is 100%, the image area ratio of the maximum density is limited to 80%, and FIG. Is output, and the toner amount (TMA) when the maximum density is 100% is limited to 3.5 g / m ² , so that the gloss of the transparent toner portion is lowered as shown in FIG. Thus, the difference between the gloss of the transparent toner portion of the gloss unevenness and the gloss of the chromatic color toner portion can be reduced, the occurrence of the gloss unevenness can be suppressed, and the toner at the position where the transparent toner and the chromatic color toner overlap. It is also possible to suppress moire patterns resulting from the periodic occurrence of scattering.

Example 1
Next, the present inventor uses a full-color printer as shown in FIG. 2, and the full-color printer is equipped with a mode for outputting a photographic image using transparent toner and a mode for outputting embossed paper. An image was formed, and the gloss difference in the image was visually confirmed.

When outputting a photographic image, transparent toner is used to reduce the gloss difference in the image, and the toner of the transparent toner necessary to reduce the gloss difference, which is the difference in gloss between the image area and the blank paper area As shown in FIG. 12, an amount of 3.5 g / m ² is sufficient as shown in FIG. 12. However, when embossed paper is output, the occurrence of image quality defects at the time of secondary transfer is prevented (the image quality defect occurrence grade is set). As shown in FIG. 13, a toner amount of 4.5 g / m ² is required and the required amount of transparent toner differs depending on the mode.

Therefore, when outputting a photographic image, the quality of the gloss difference becomes excessive, but the maximum toner amount of the transparent toner is fixed at 4.5 g / m ² so that the image quality can be guaranteed regardless of which mode. Is set.

  However, when outputting a photographic image, as described above, it is possible to suppress the occurrence of uneven glossiness, which is the difference between the gloss of the transparent toner portion and the gloss of the chromatic color toner portion, and the transparent toner and chromatic color toner It is also necessary to suppress moiré patterns resulting from the periodic occurrence of toner scattering at overlapping positions.

Therefore, in the first embodiment, as shown in FIG. 1, the maximum toner amount is fixed at 4.5 g / m ² , and when embossed paper is output, the maximum area ratio is 100%. When outputting a photographic image, by setting the maximum area ratio to 80%, it is possible to suppress the occurrence of uneven glossiness, which is the difference between the gloss of the transparent toner portion and the gloss of the chromatic toner portion, and the transparent toner. Further, the moire pattern caused by the periodic occurrence of toner scattering at the position where the chromatic color toner overlaps is also suppressed.

Example 2
Next, the present inventor uses a full-color printer as shown in FIG. 2, and the full-color printer is equipped with a mode for outputting a photographic image using transparent toner and a mode for outputting embossed paper. An image was formed, and the difference in gloss and the occurrence of a moire pattern in the image were confirmed visually.

  When manufacturing a full-color printer as shown in FIG. 2, it has been found that the beam diameter of the laser beam of the image exposure device 6 varies within a range of about 40 μm to 90 μm due to semiconductor laser or optical system component errors. .

  When the beam diameter of the laser beam is increased, toner followability with respect to the electrostatic latent image is deteriorated, so that the toner is likely to be scattered even with the same screen line number. As a result of experiments by the present inventors, a relationship between the beam diameter of the laser beam and the number of screen lines was obtained as shown in FIG.

  In FIG. 14, ◯ indicates that no moire has occurred, and x indicates that moire has occurred. The condition in which the moire did not occur is that a relational expression of L ≧ −1.4R + 391 is obtained when the beam diameter R of the laser beam for forming the electrostatic latent image on the photosensitive drum 4 and the number of screen lines are L. It is done. That is, moire means that it occurs in the shaded area.

  Therefore, in the second embodiment, the beam diameter of the laser beam of the image exposure apparatus 6 is measured, and the number of screen lines is set so as to satisfy the relational expression L ≧ −1.4R + 391 according to the beam diameter R of the laser beam. L is set.

Example 3
As described above, the beam diameter of the laser beam of the image exposure apparatus 6 generally varies between 40 μm and 90 μm including variation. Therefore, the number of screen lines is preferably set to 340 lines or more in consideration of the relational expression L ≧ −1.4R + 391.
Therefore, in the third embodiment, the screen line number L of the image exposure apparatus 6 is set to 340 lines or more, specifically 400 lines.

FIG. 1 is a block diagram showing an image processing apparatus of a tandem type full color printer as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is an overall configuration diagram showing a tandem type full-color printer as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a block diagram showing an image forming unit of a tandem type full color printer as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 4 is a block diagram showing an image processing apparatus of a tandem type full-color printer as the image forming apparatus according to Embodiment 1 of the present invention. FIG. 5 is a schematic diagram showing a dither matrix. FIG. 6 is a schematic diagram showing a dither matrix. FIG. 7 is a schematic diagram showing a dither matrix. FIG. 8 is a schematic diagram showing a dither matrix. FIG. 9 is a graph showing the area ratio of the transparent toner image. FIG. 10 is a schematic diagram showing a dither matrix. FIG. 11 is a schematic diagram showing an image composed of transparent toner and chromatic color toner. FIG. 12 is a graph showing experimental results. FIG. 13 is a graph showing experimental results. FIG. 14 is a graph showing experimental results. FIG. 15 is a schematic diagram showing an image composed of a conventional transparent toner and chromatic color toner. FIG. 16 is a schematic diagram showing an image composed of a conventional transparent toner and chromatic color toner.

Explanation of symbols

  60: Mode setting button 61: Photo image output ROM 62: Embossed paper output ROM

Claims (5)

Image forming means for forming an image made of at least one chromatic toner and an image made of transparent toner;
Transfer means for transferring an image made of at least one chromatic toner formed by the image forming means and an image made of transparent toner onto a recording medium so that the image made of transparent toner is positioned on the uppermost layer;
When forming an image by the image forming means, a first mode in which a transparent toner is used to form an image on the recording medium having an uneven surface, and a transparent toner is used to reduce a gloss difference in the image. Mode setting means for setting a plurality of different modes including the second mode to be used ;
According to the mode set by the mode setting means, the maximum density image area ratio when forming the image made of the transparent toner is changed so that the second mode is lower than the first mode. An image forming apparatus comprising: an image forming condition changing unit. Multi-tone image data corresponding to at least one chromatic color is converted into halftone image data having a predetermined number of gradations using a screen, and multi-tone image data corresponding to transparency is Data conversion means for converting into halftone image data of a predetermined number of gradations using a screen having a larger number of screen lines than a chromatic toner screen;
Image forming means for forming an image made of at least one chromatic toner and an image made of transparent toner based on halftone image data corresponding to at least one chromatic color and transparency converted by the data conversion means; ,
Transfer means for transferring an image made of at least one chromatic toner formed by the image forming means and an image made of transparent toner onto a recording medium so that the image made of transparent toner is positioned on the uppermost layer;
When forming an image by the image forming means, a first mode in which a transparent toner is used to form an image on the recording medium having an uneven surface, and a transparent toner is used to reduce a gloss difference in the image. Mode setting means for setting a plurality of different modes including the second mode to be used;
In accordance with the mode set by the mode setting means, the image area ratio of the maximum density when forming an image made of the transparent toner is changed so that the second mode is lower than the first mode. An image forming apparatus comprising: an image forming condition changing unit .   3. The image forming apparatus according to claim 1, wherein the number of screen lines of the laser beam that forms an electrostatic latent image by performing image exposure on the photoreceptor of the image forming unit is determined by the beam diameter of the laser beam. An image forming apparatus, wherein the image forming apparatus is set to decrease as the size increases.   4. The image forming apparatus according to claim 3, wherein the number of screen lines of laser light for forming an electrostatic latent image by performing image exposure on the photoreceptor of the image forming means is L, and the beam diameter of the laser light is R. In this case, the image forming apparatus satisfies the relationship L ≧ −1.4R + 391.   5. The image forming apparatus according to claim 1, wherein the number of screen lines when forming the transparent toner image is set to 340 lines or more.

Images