JP2007240720A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the amount of toner wasted without being transferred onto a recording paper by changing settings of toner image sizes larger than recording paper sizes of the front, rear, left, and right end parts of the recording paper according to the kind and water content of the recording paper when borderless printing is performed. <P>SOLUTION: The image forming apparatus forms a toner image so that an excessive image area corresponding to the front end of the recording paper and an excessive image area corresponding to the rear end of the recording end, and an excessive image area corresponding to the left end of the recording paper and an excessive image area corresponding to the left end of the recording paper may be different in size from each other when an excessive image which is not transferred to the recording paper P is formed during borderless printing. Then the image forming apparatus is configured to detect the kind and water content of the recording paper P by a recording paper kind sensor 61 and a water sensor 51 as well as the printing mode, and then change the sizes of the excessive image areas corresponding to the front end, rear end, right end, and left end of the recording paper P according to detection results. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus using an electrophotographic method such as a printer, a copying machine, or a facsimile having a double-sided image forming function and a borderless printing function on a recording medium.

  Conventionally, in an inkjet type or electrophotographic type image forming apparatus, an image is recorded with a margin margin at a peripheral portion of a recording medium (hereinafter referred to as a recording sheet). However, with the colorization of image forming apparatuses, there is an increasing demand for so-called borderless printing that can record an image with no margins over the entire area of the recording paper, similar to the printing of silver halide photographs. In the inkjet image forming apparatus, products capable of borderless printing have already been put on the market, and an electrophotographic image forming apparatus has also been proposed as in Patent Document 1.

  For example, in the case of an electrophotographic color image forming apparatus employing an intermediate transfer body method, a toner image formed on the intermediate transfer body is transferred onto a recording sheet by the transfer device. FIG. 8A shows the size of the toner image T formed on the intermediate transfer member, where Iv is vertical and Ih is horizontal. FIG. 8B shows the size of the recording paper P, where Pv is vertical and Ph is horizontal. In general printing with margins having margins, the relationship between the size of the toner image T and the size of the recording paper P is Iv <Pv, Ih <Ph, and as shown in FIG. A toner image T having a margin (margin) on P is finally output. On the other hand, when performing borderless printing, a toner image T having the same size as that of the recording paper P may be formed on the intermediate transfer member as shown in FIG. That is, the size of the toner image T is set so that the relationship between the size of the toner image T and the size of the recording paper P is Iv = Pv and Ih = Ph. Then, a toner image T having no margin (margin) on the recording paper P is finally output.

  However, when the size of the toner image T and the size of the recording paper P are the same, a margin is generated at the upper end portion of the recording paper P if the feeding timing of the recording paper P is slightly early, and a margin is formed at the lower end portion if it is slightly late. Will occur. Further, when the recording paper P is slightly shifted left and right, a margin is generated at the left end or the right end. FIG. 10A shows a case where the recording paper P is fed with a delay in feeding timing and shifted to the right. As shown in FIG. 10B, a margin is generated on the recording paper P. The desired borderless image is not obtained. In order to transfer the toner image T onto the recording paper P without margins, perfect paper feeding accuracy is required. However, the toner image T is supplied perfectly in accordance with changes in the material, moisture absorption state, atmosphere environment, etc. of the recording paper P. It is difficult to make paper. Therefore, when performing borderless printing, a toner image T that is slightly larger than the recording paper P is formed on the intermediate transfer member, and even if the recording paper P is fed slightly off the front, back, left and right, The toner image T is a borderless image.

That is, the size of the toner image T is set so that the relationship between the size of the toner image T and the size of the recording paper P satisfies Iv> Pv and Ih> Ph. FIG. 11A shows the relationship between the size of the toner image T and the size of the recording paper P when Iv> Pv and Ih> Ph. As shown in FIG. 11B, even if the recording paper P is fed slightly deviated from front to back and left and right, it is within the size of the toner image T, so that no margin is generated on the recording paper P.
JP 2004-005559 A

  However, in the conveyance of the recording paper, the toner image formed on the intermediate transfer member can be accurately transferred to the recording paper at the timing when the recording paper passes the registration sensor at the leading edge of the recording paper. On the other hand, regarding the trailing edge of the recording paper, the transportability and the skew feeding amount differ depending on the type of recording paper and the amount of moisture contained therein, and a margin may be generated.

  In addition, with respect to the lateral direction of the recording paper, a configuration in which the recording paper is abutted against the right end or the left end during double-sided printing and transported is well known. In the case of the above configuration, the toner image formed on the intermediate transfer member can be transferred with high accuracy at the abutted right end or left end. On the other hand, with respect to the end portion that is not abutted, the transportability and the expansion / contraction rate of the recording paper differ depending on the type of recording paper and the amount of moisture contained therein, and a margin may be generated.

  Further, as described above, since the size of the toner image T is larger than the size of the recording paper P, residual toner that is not transferred to the recording paper P is generated. FIG. 12 shows the toner remaining on the intermediate transfer member without being transferred to the recording paper P. This residual toner is a wasteful consumption toner, and a problem of a capacity of a container for storing the residual toner occurs due to an increase in the residual toner. Therefore, a means for reducing the residual toner as much as possible must be taken.

  The present invention has been made paying attention to the above points, and it is an object of the present invention to provide an image forming apparatus that reduces the amount of toner that is not transferred onto recording paper and is wasted when performing borderless printing. Objective.

  In order to solve the above problems, an image forming apparatus of the present invention has the following configuration.

  (1) Image forming means for forming an image on an image carrier, a transfer member for carrying an image formed on the image carrier, and an image formed on the image carrier on the transfer member When forming an image on the image carrier by the first transfer means for transferring the image, the second transfer means for transferring the image transferred on the transfer member to a recording medium, and the image forming means, An image forming apparatus capable of forming an image on the entire area of the recording medium, the surplus image forming unit forming an untransferred surplus image on the recording medium by the second transfer unit on the transfer member; The surplus image forming means differs in the size of the surplus image area corresponding to the leading end of the recording medium and the size of the surplus image area corresponding to the trailing end of the recording medium based on the type of the recording medium. On the image carrier Image forming apparatus and forming the.

  According to the present invention, when image formation is performed on the entire area of the same recording sheet, and an excessive image that is not transferred to the recording sheet is formed, an optimum amount is recorded on the leading end of the recording sheet and the trailing end of the recording sheet. A toner image can be formed on the intermediate transfer body more than the sheet, and as a result, the amount of toner that is not transferred onto the recording sheet and is wasted can be reduced.

  Further, the toner image can be formed on the intermediate transfer body more than the recording paper by the optimum amount with respect to the right edge of the recording paper and the left edge of the recording paper, and as a result, the amount of toner that is not transferred onto the recording paper and is wasted is reduced. be able to.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  The configuration of the image forming apparatus of this embodiment will be described with reference to the schematic cross-sectional view of the full-color electrophotographic image forming apparatus shown in FIG. Here, as the image carrier, a plurality of photosensitive drums 11a, 11b, and 11c corresponding to respective color toners of the first color: yellow, the second color: magenta, the third color: cyan, and the fourth color: black. , 11d. Further, as a transfer member, it has an intermediate transfer belt 1 that is in contact with each of the photosensitive drums 11a, 11b, 11c, and 11d at each primary transfer portion.

  Each photosensitive drum is a first color (yellow) photosensitive drum 11a located at the most upstream position along the moving direction of the intermediate transfer belt 1, and a second color (closest downstream of the photosensitive drum 11a). A magenta photosensitive drum 11b is disposed. In addition, the third color (cyan) photosensitive drum 11c located closest to the downstream side of the photosensitive drum 11b, and the fourth color (black) photosensitive drum positioned closest to the downstream side of the photosensitive drum 11c. They are arranged in the order of 11d.

  Photosensitive drums 11a, 11b, 11c, and 11d in this embodiment have an outer diameter of 30.0 mm and have a layer in which a photosensitive material is applied on an aluminum cylinder.

  For the intermediate transfer belt 1, a resin film such as a urethane resin, a fluorine resin, a nylon (registered trademark) resin, or a polyimide resin can be used. In addition, a resin film in which carbon or conductive powder is dispersed in these resins to adjust the resistance, or a multi-layer structure in which a resin layer is formed as a release layer on the toner carrier surface side of a base layer sheet such as urethane rubber or NBR It is also possible to use an elastomer sheet having

The intermediate transfer belt 1 used in the present embodiment is formed in the intermediate transfer belt 1 in a transfer process or the like by dispersing carbon in polyimide and adjusting the medium resistance to a surface resistivity ρs = 1 × 10 ¹² Ω. The added charge can be attenuated without providing a special static elimination mechanism. The intermediate transfer belt 1 is a single-layer endless belt having a circumferential length of 1000 mm and a thickness of 100 μm.

  The surface resistivity measurement is based on JIS-K6911. After obtaining good contact between the electrode and the surface of the intermediate transfer belt 1 by using conductive rubber as an electrode, an ultrahigh resistance resistance meter (R8340 manufactured by Advantest Corporation) is used. ). The measurement conditions were applied voltage = 100 V and voltage application time = 30 s.

  As shown in FIG. 1, the intermediate transfer belt 1 is suspended by three rollers including a drive roller 1a, a support roller 1b, and a separation roller 1c included in the intermediate transfer belt 1. The drive roller 1a, the support roller 1b, and the separation roller 1c are electrically grounded.

The driving roller 1a and the separation roller 1c are rollers having an outer diameter of 29.8 mm composed of an aluminum cored bar having a diameter of 24.0 mm and a hydrin rubber layer having a layer thickness of 2.9 mm, and the resistance is adjusted by adjusting the resistance of the hydrin rubber. The resistance value is 1 × 10 ⁶ Ω.

  The support roller 1b is an aluminum roller having a diameter of 29.8 mm.

  The roller resistance value was measured using an ultra-high resistance resistance meter (R8340 manufactured by Advantest) while the roller to be measured was brought into contact with an aluminum cylinder having a diameter of 30 mm and rotated following the aluminum cylinder. The measurement conditions were applied voltage = 100 V, voltage application time = 30 s, contact force = 9.8 N, and rotational peripheral speed = 117 mm / s.

  The intermediate transfer belt 1 is rotated at a predetermined process speed (117.0 mm / s in this embodiment) by a driving device (not shown) in the direction of the arrow. The photosensitive drums 11a, 11b, 11c, and 11d are 99.0% of the moving speed of the intermediate transfer belt 1 in the same direction as the moving direction of the intermediate transfer belt 1 (115.8 mm / s in this embodiment). And is rotated by a driving device (not shown). The primary transfer efficiency is improved by giving a speed difference ΔVa to the moving speed of each of the photosensitive drums 11a, 11b, 11c, and 11d and the intermediate transfer belt 1. However, as the speed difference ΔVa between the moving speeds of the photosensitive drums 11a, 11b, 11c, and 11d and the intermediate transfer belt 1 is larger, the photosensitive drums 11a, 11b, and 11c are caused by the friction with the intermediate transfer belt 1. , 11d wear and scratches are promoted. Therefore, in this embodiment, the speed difference ΔVa is set to 1.5% of the process speed (1.8 mm / s in this embodiment) in order to achieve both the primary transfer efficiency and the degree of wear and scratches on the photosensitive drum.

  The photosensitive drums 11a, 11b, 11c, and 11d are uniformly charged by the contact charging rollers 12a, 12b, 12c, and 12d. Then, an electrostatic latent image is created by laser light from each of the scanners 13a, 13b, 13c, and 13d (corresponding to image forming means) modulated by the exposure information signal.

  The image information signal sent from the host computer 100 is processed by the controller 200 (corresponding to the surplus image forming means) so as to obtain a desired size, and converted into an exposure information signal. Further, the controller 200 selects different image forming conditions depending on the type of recording paper as the image forming selection means.

  The intensity of the laser beam and the irradiation spot diameter are appropriately set according to the resolution of the image forming apparatus and the desired image density. The electrostatic latent images on the respective photosensitive drums 11a, 11b, 11c, and 11d are formed by holding the portion irradiated with the laser light at the bright portion potential VL (about −150V). The portion not irradiated with the laser beam is formed by being held at a dark portion potential VD (about −650 V) charged by each of the contact charging rollers 12a, 12b, 12c, and 12d as primary chargers.

  The electrostatic latent images reach the facing portions of the developing units 14a, 14b, 14c, and 14d by the rotation of the photosensitive drums 11a, 11b, 11c, and 11d. Then, developer (toner) charged with the same polarity as the surface of the photosensitive drum (minus polarity in this embodiment) is supplied to be visualized to form a developer image (toner image).

  The developing device 14 in this embodiment is a developing device that employs a two-component developing system. Further, the developing bias in this embodiment is a bias in which an AC voltage is superimposed on a DC voltage of DC component = −400 V, AC component = 1.5 kVpp, frequency = 3 kHz, waveform = rectangular wave.

  The toner images formed on the photosensitive drums 11a, 11b, 11c, and 11d are transferred onto the intermediate transfer belt 1 by a primary transfer bias (in this embodiment, constant voltage control of +400 V). The primary transfer bias is applied from primary transfer bias sources 16a, 16b, 16c, and 16d to primary transfer rollers 15a, 15b, 15c, and 15d (corresponding to a first transfer unit) that are in contact with the back surface of the intermediate transfer belt 1. . Note that this transfer is performed at each primary transfer nip which is a proximity or contact portion between the intermediate transfer belt 1 and the photosensitive drums 11a, 11b, 11c, and 11d.

  When the intermediate transfer belt 1 passes through the primary transfer nip with the photosensitive drum 11d, the formation of the four-color image on the intermediate transfer belt 1 is completed, and the primary transfer process is completed.

  On the other hand, the surface of each of the photosensitive drums 11a, 11b, 11c, and 11d after the primary transfer of the toner image is subjected to removal of primary transfer residual toner and the like by a drum cleaning device 17a, 17b, 17c, and 17d made of a urethane rubber blade. To be cleaned. In preparation for the next image forming process.

  Next, one sheet of recording paper P is taken out from the recording paper cassette 5 by the paper feeding means 6, and a portion between the separation roller 1c sandwiching the intermediate transfer belt 1 and the secondary transfer roller 2 as the second transfer means. Is inserted into the secondary transfer nip portion.

  At this time, the secondary transfer bias source 21 applies an optimum bias that is opposite in polarity to the toner and is determined according to the temperature and humidity in the image forming apparatus detected by the temperature and humidity sensor 52 to the secondary transfer roller 2. In this embodiment, 15 ° C./10% R.D. H. Sometimes +20 μA, 23 ° C./50% R.D. H. Sometimes +30 μA, 30 ° C./80% R.D. H. Sometimes it is constant current control of +35 μA. Thereafter, the toner image is secondarily transferred from the intermediate transfer belt 1 to the recording paper P.

The secondary transfer roller 2 in the present embodiment is a roller having an outer diameter of 22.0 mm composed of an aluminum cored bar having a diameter of 14.0 mm and a foamed hydrin rubber layer having a layer thickness of 4 mm, and resistance adjustment of the hydrin rubber is performed. The roller resistance value is 1 × 10 ⁸ Ω. The hardness of the secondary transfer roller 2 is 35 ° (ASKER-C).

  The secondary transfer roller 2 is rotated at a substantially constant speed with the intermediate transfer belt 1 by a driving device (not shown) in the direction of the arrow, so that the recording paper P can be fed at a predetermined process speed (the actual speed) regardless of the amount of toner on the intermediate transfer belt 1. In the embodiment, it is stably conveyed at 117.0 mm / s). In addition, it is possible to obtain an image size on the recording paper P that is equal to the image size formed on the intermediate transfer belt 1 without depending on the image pattern.

  The toner adhering to the secondary transfer roller 2 is cleaned by the secondary transfer roller cleaner 22 having a cleaning blade made of urethane rubber to prevent the toner from adhering to the back surface of the recording paper P.

  The recording paper P on which the unfixed toner image that has passed through the secondary transfer nip portion reaches the fixing device 3 and is heated and pressurized to obtain a permanent fixed image. The recording paper P discharged from the fixing device 3 is transported by a transport means 7 to a paper discharge tray 8 outside the image forming apparatus.

  After the transfer of the toner image onto the recording paper P, the surface of the intermediate transfer belt 1 is cleaned of secondary transfer residual toner by an intermediate transfer body cleaner 4 having a cleaning blade made of urethane rubber.

  Further, when image formation is performed on both sides of the recording paper P, the recording paper P discharged from the fixing device 3 through the first image forming process is conveyed again to the paper feeding means 6 by the conveying means 7. Then, after being discharged from the fixing device 3 through the second image forming process, the paper is conveyed by the conveying means 7 to the paper discharge tray 8 outside the image forming apparatus.

  Here, the recording paper type sensor 61 (corresponding to the recording medium type detecting means) will be described with reference to FIG. The recording paper type sensor 61 includes an LED 611 that emits light for reading the surface property of the recording paper P, and an LED 616 that emits light for reading the transparency of the recording paper P. Further, it has a CMOS area sensor 612 that reads and outputs the surface property of the recording paper P by the LED 611 as an image in the light irradiation area, an LED lens 613, and a CMOS area sensor lens 614. Further, the LED 616 includes a CMOS area sensor 618 that reads and outputs the transparency of the recording paper P as an image in the light irradiation area, an LED lens 617, and a CMOS area sensor lens 619. And it has the diffusion plate 615 for diffusing transmissive LED light.

  The light emitted from the LED 611 is emitted obliquely to the recording paper P through the LED lens 613. The reflected light from the recording paper P is collected through the CMOS area sensor lens 614 and focused on the CMOS area sensor 612, thereby reading the surface image of the recording paper P. Since the light emitted from the LED 611 is obliquely applied to the recording paper P, a shadow is formed according to the unevenness of the surface of the recording paper P. Therefore, the gloss of the recording paper P is determined from the average light amount of the image read by the CMOS area sensor 612. It becomes possible to detect the degree. In addition, the depth of unevenness on the surface of the recording paper P can be detected from the difference between the maximum value and the minimum value of the contrast of the image read by the CMOS area sensor 612. Furthermore, it is possible to detect the interval between the irregularities on the surface of the recording paper P from the number of edges of the binarized image read by the CMOS area sensor 612.

  The light emitted from the LED 616 is irradiated perpendicularly to the recording paper P via the LED lens 617 and the diffusion plate 615. The transmitted light from the recording paper P is collected through the CMOS area sensor lens 619 and imaged on the CMOS area sensor 618, thereby reading the transmitted image on the recording paper P. The light emitted from the LED 616 passes through the recording paper P, and the transmittance of the recording paper P can be detected from the average light amount of the image read by the CMOS area sensor 618.

  FIG. 4 shows a simple configuration of the recording paper type sensor 61 in FIG. The CMOS area sensor 612 that reads and outputs the light irradiation area as an image and the CMOS area sensor lens 614 are used in combination with the transmission type. That is, the CMOS area sensor 618 that reads and outputs the light irradiation area as an image and the CMOS area sensor lens 619 are used to read the surface property of the recording paper P by the LED 611 and the transparency of the recording paper P by the LED 616.

  By detecting the glossiness and transparency of the recording paper P, and the depth and spacing of the surface irregularities, many recording paper types such as plain paper, thick paper, rough paper, coated paper, OHT, and resin film according to the classifications listed in Table 1 Can be detected.

  Next, borderless printing (corresponding to image formation over the entire area of the recording medium) in the present invention will be described. A feature of the present invention is that when performing borderless printing, the leading edge of the recording sheet of the toner image formed on the intermediate transfer belt 1 and the recording sheet so that the optimum residual toner amount is obtained at the leading edge of the recording sheet and the trailing edge of the recording sheet. The amount of protrusion to the recording paper at the trailing edge is set differently.

  When the user selects borderless printing for the image file on the host computer 100, the controller 200 resizes the image so that borderless printing is performed for the selected recording paper size. The resized image size is set to be slightly larger than the selected recording paper size so that no margin is generated on the recording paper P. FIG. 2 shows the resized toner image T size formed on the intermediate transfer belt 1 and the size of the recording paper P (hereinafter simply referred to as recording paper size). The length in the recording sheet conveyance direction of the toner image T that is larger than the recording sheet size at the leading end of the recording sheet is Iv1 (corresponding to the size of the surplus image area corresponding to the leading end of the recording medium). The length of the toner image T in the recording sheet conveyance direction, which is larger than the recording sheet size at the trailing end of the recording sheet, is Iv2 (corresponding to the size of the surplus image area corresponding to the trailing end of the recording medium). Further, the length of the recording paper P in the recording paper conveyance direction is Pv. The frame-like toner image T as shown in FIG. 2 becomes the secondary transfer residual toner that is wasted.

  The conditions for determining the length Iv1 in the recording sheet conveyance direction of the toner image T larger than the recording sheet size at the leading end of the recording sheet will be described below. The recording paper P is adjusted to have a toner image T on the intermediate transfer belt 1 on the recording paper P by adjusting the conveyance timing by a registration sensor (not shown) arranged before the secondary transfer roller 2. Secondary transfer is performed at the position of. That is, the length Iv1 of the toner image T at the leading end of the recording paper in the recording paper conveyance direction is the maximum amount of deviation caused by the skew of the recording paper P or the difference in behavior of the recording paper P from the registration sensor to the secondary transfer. Value.

  The conditions for determining the length Iv2 of the toner image T in the recording sheet conveyance direction larger than the recording sheet size at the rear end of the recording sheet are as follows. That is, an amount larger than the length Iv1 in the recording sheet conveyance direction of the toner image T at the leading end of the recording sheet is set for the recording sheet size set as shown in FIG. For example, the recording paper type margin is added, and the relationship is Iv1 <Iv2. The margin of the recording paper type varies depending on the difference in transportability associated with the type of recording paper P. For example, if the glossiness of coated paper or the like is high, slipping of the recording paper P may occur. Therefore, the set amounts of Iv1 and Iv2 are set larger than the set amount of plain paper. Further, since the skew of the recording paper P may deteriorate if the density is high, such as thick paper, the set amounts of Iv1 and Iv2 are made larger than the set amount of plain paper.

  Further, the length Iv2 of the toner image T in the recording sheet conveyance direction that is larger than the recording sheet size at the trailing edge of the recording sheet is determined to be reprinted because the recording sheet size does not match the set recording sheet size. The recording paper size may be the same. With the above setting, no margin is generated at the rear end of the recording paper P with respect to the printable size. In addition, it is possible to form an image with a minimum amount of toner while satisfying the condition that no margin is generated at the trailing edge of the recording paper P.

  In the case where the recording paper size is not set, the margin is not generated by setting the size of the toner image T to the maximum recording paper size.

  Next, a second embodiment of the present invention will be described. Constituent elements similar to those of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the first embodiment, the size of the toner image T in the conveyance direction of the recording paper P (hereinafter simply referred to as toner image size) has been described. In this embodiment, the toner image size in the direction perpendicular to the conveyance direction of the recording paper P will be described.

  FIG. 2 shows the resized toner image size and recording paper size formed on the intermediate transfer belt 1. The length in the direction perpendicular to the recording sheet conveyance direction of the toner image T larger than the recording sheet size at the left end portion of the recording sheet is defined as Ih1 (corresponding to the size of the surplus image area corresponding to the left end of the recording medium). Further, the length of the toner image T in the direction perpendicular to the recording sheet conveyance direction that is larger than the recording sheet size at the right end of the recording sheet is defined as Ih2 (corresponding to the size of the excess image area corresponding to the right end of the recording medium). The length of the recording paper P in the direction perpendicular to the recording paper conveyance direction is Ph. The frame-like toner image T as shown in FIG. 2 becomes the secondary transfer residual toner that is wasted.

  At the time of image formation for double-sided printing, the recording paper P on which the toner image T is formed is fixed by the fixing device 3 and then sent again to the paper feeding unit to form the toner image T on the back surface. While being sent to the paper feeding unit again, the recording paper P may be carried against the rightmost or leftmost edge in a direction perpendicular to the conveyance direction of the recording paper P of the image forming apparatus main body. In this case, the image in the direction perpendicular to the conveyance direction of the recording paper P on the back surface is resized by adding a margin so that the image corresponding to the recording paper size is borderless with respect to the rightmost edge or the leftmost edge. .

  For example, in the configuration in which the recording paper P hits the leftmost end, the length Ih1 of the toner image T larger than the recording paper size at the left end of the recording paper in the direction perpendicular to the recording paper conveyance direction is equal to the skew of the recording paper P. The size is considered. On the other hand, the length Ih2 of the toner image T, which is larger than the recording paper size at the right end of the recording paper, in the direction perpendicular to the recording paper conveyance direction is a size obtained by adding the skew of the recording paper P and the margin of the recording paper type. Thus, the relationship of Ih1 <Ih2 is established. The margin of the recording paper type varies depending on the difference in transportability that accompanies different recording paper types and the amount of shrinkage of the recording paper P once it passes through the fixing. For example, since recording paper such as thick paper may deteriorate in skew, the set amounts of Ih1 and Ih2 are made larger than those of plain paper. Further, since the shrinkage amount of the recording paper is small when the density of the resin film or the like is high, the set amounts of Ih1 and Ih2 are set to the same set amounts as those for the front surface recording. Further, since the amount of shrinkage is large for thin paper, rough paper, and the like, the set amounts of Ih1 and Ih2 are made smaller than those for recording on the front surface. Thus, by appropriately selecting the set amount according to the paper type, the toner is wasted without being transferred onto the recording paper by changing the margin corresponding to the transportability and the expansion / contraction rate according to the recording paper type. The amount can be kept small.

  Next, a third embodiment of the present invention will be described. FIG. 1 is a schematic cross-sectional view of an electrophotographic image forming apparatus in Example 3. Constituent elements similar to those in the first and second embodiments are denoted by the same reference numerals and description thereof is omitted.

  In the first and second embodiments, the method of setting the toner image size larger than the recording paper size at the front end, rear end, left end, and right end of the paper has been described using the recording paper type sensor 61. However, if there is a means for measuring the moisture content of the recording paper P to be fed, the set value of the toner image size larger than the recording paper size can be obtained more accurately. For this reason, even if the recording paper P is fed slightly deviated from front to back and left and right, no margin is generated in the recording paper P, and the amount of secondary transfer residual toner can be further reduced.

  The recording sheet cassette 5 is provided with a moisture sensor 51 (corresponding to a moisture amount detecting means) that detects the moisture content of the recording sheet P.

  As a method for measuring the moisture content of the recording paper P, there are generally a method for measuring the resistance value of the recording paper P, an optical method, and the like. In this embodiment, since the measurement can be performed in a non-contact manner, the moisture content of the recording paper P is measured by measuring the reflection intensity from the recording paper P of infrared rays having a specific wavelength absorbed by water molecules. An infrared optical moisture sensor was used as the moisture sensor 51. Since the optical sensor is capable of non-contact measurement, it is possible to suppress measurement variations caused by contamination of the measurement probe due to repeated image formation as compared with a method of measuring the resistance value of the recording paper P. .

  The moisture sensor 51 will be described with reference to FIG. The moisture sensor 51 includes an incandescent light bulb 511 that irradiates light on the surface of the recording paper P, and two photodiodes 512 and 513 that receive light reflected by the incandescent light bulb 511 on the surface of the recording paper P, and read and output the amount of reflected light. Light emitted from the incandescent bulb 511 is applied to the recording paper P. Reflected light from the recording paper P is received by the photodiodes 512 and 513. The two photodiodes 512 and 513 are provided with optical filters having different characteristics, so that the wavelengths of light to be detected are different. The photodiode 512 detects the amount of reflected light having a wavelength in the vicinity of 1.5 μm and 1.9 μm corresponding to the water absorption region, and the photodiode 513 in the visible light region (0.4 μm to 1.0 μm). By calculating the detected light amount information of these two photodiodes 512 and 513, the moisture content of the recording paper P can be measured.

  The two photodiodes 512 and 513 can also measure the moisture content of the recording paper P by adopting a configuration in which the light irradiated from the incandescent light bulb 511 is received through the recording paper P.

  Further, at the time of image formation for double-sided printing, the recording paper P on which the toner image T is formed is fixed by the fixing device 3 and then sent again to the paper feeding unit in order to form the toner image T on the back surface. The recording paper P once fixed by the fixing device 3 expands and contracts as the moisture of the recording paper P evaporates.

  The expansion / contraction rate of the recording paper P differs depending on the moisture content and the type of the recording paper P. For example, high-density recording paper such as coated paper or resin film has a small expansion / contraction rate regardless of the moisture content, so set the set amounts for the front, rear, left, and right edges of the paper to be the same as when recording on the front side. . On the other hand, low-density recording paper, such as rough paper, has different expansion / contraction rates depending on the moisture content, and the length of the recording paper transport direction and the direction perpendicular thereto differ, so the leading, trailing, left, and right edges of the paper Is set to a different amount than when recording on the front side.

  In addition, the curl varies depending on the type of recording paper and the amount of water contained. In general, thin paper or the like has a high moisture content, and when the density is low, the amount of moisture taken away by the fixing device 3 is large, so that bending (curl) tends to deteriorate. That is, since the conveyance performance deteriorates due to the bending (curl) of the recording paper P, the set amounts of the leading edge, the trailing edge, the left edge, and the right edge of the recording paper are made larger than those of the plain paper.

  Therefore, in the third embodiment, by changing the setting of the toner image size larger than the recording paper size at the leading edge, the trailing edge, the left edge, and the right edge of the recording paper from the detection results of the recording paper type sensor 61 and the moisture sensor 51. The amount of residual transfer residual toner can be suppressed.

  Even in an image forming apparatus that does not include the recording paper type sensor 61, the setting of the toner image size larger than the recording paper size at the leading edge, trailing edge, left edge, and right edge of the recording paper may be changed depending on each printing mode. Is possible.

  Next, a fourth embodiment of the present invention will be described. FIG. 6 is a schematic cross-sectional view of the electrophotographic image forming apparatus according to the fourth embodiment. The same components as those in the first embodiment, the second embodiment, and the third embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the third embodiment, the moisture content of the recording paper P is measured by the moisture sensor 51. However, since the moisture sensor is expensive, it is difficult to increase the cost. Therefore, instead of the detection result of the moisture sensor 51, the temperature / humidity sensor 52 is used as the moisture amount detection means, and the moisture content is determined using the detection result of the temperature / humidity sensor 52. The moisture sensor 51 is necessary to strictly detect the moisture content of the recording paper P, but there is a correlation between the temperature and humidity of the recording paper P leaving environment and the moisture content of the recording paper P. For this reason, even if the moisture content is determined using the detection result of the temperature / humidity sensor 52 instead of the detection result of the moisture sensor 51, the approximate effect of the present invention can be obtained.

  Therefore, in the fourth embodiment, by changing the setting of the toner image size larger than the recording paper size at the front end, rear end, left end, and right end of the recording paper, based on the detection results of the recording paper type sensor 61 and the temperature / humidity sensor 52. The amount of secondary transfer residual toner can be suppressed.

  The color image forming apparatus adopting the intermediate transfer belt system has been described above. However, the intermediate transfer drum system, the electrostatic transfer body system, the color image forming apparatus employing the multiple development system, and the monocolor image forming apparatus. The same effect can be obtained when performing borderless printing.

1 is a schematic sectional view of an image forming apparatus according to Embodiment 1 of the present invention. A diagram for explaining the size relationship between a toner image and recording paper during borderless printing 1 is a schematic cross-sectional view illustrating a recording paper type sensor according to a first embodiment of the invention. 1 is a schematic cross-sectional view illustrating a simple recording paper type sensor according to a first embodiment of the invention. Schematic sectional view for explaining a moisture sensor according to Example 3 of the present invention Schematic sectional view of an image forming apparatus according to Embodiment 4 of the present invention. FIG. 6 is a diagram illustrating a size relationship between a toner image and recording paper during borderless printing according to the first embodiment of the present invention. 2A and 2B are diagrams for explaining the size relationship between a toner image and recording paper during normal printing, in which FIG. 1A shows the size of the toner image formed on the intermediate transfer member, and FIG. 2B shows the size of the recording paper; , (C) is a diagram in which a toner image having a margin (margin) on the recording paper is output. 4A and 4B are diagrams illustrating a case where the toner image and the recording paper have the same size, where FIG. 5A is a diagram illustrating the size of the toner image formed on the intermediate transfer member, and FIG. 5B is a diagram illustrating the size of the recording paper; c) A toner image having no margin (margin) on the recording paper is output. FIG. 6 is a diagram for explaining a case where the toner image and the recording paper are fed in the same size, (a) is a diagram showing a case where the feeding timing of the recording paper is delayed and is shifted to the right, and (b). FIG. 3 is a diagram showing that a desired marginless image is not obtained due to a margin on the recording paper. FIGS. 7A and 7B are diagrams illustrating a size relationship between a toner image and recording paper during borderless printing according to a conventional example, where FIG. 7A illustrates that the toner image size is larger than the recording paper size, and FIG. Diagram showing that even if the paper is fed slightly deviated left and right, it will fit within the toner image size The figure explaining the residual toner at the time of borderless printing concerning a conventional example

Explanation of symbols

1 Intermediate transfer belt (equivalent to transfer member)
1a Drive roller 2 Secondary transfer roller (corresponding to second transfer means)
5 Recording paper cassette 6 Paper feed means 7 Transport means 8 Paper discharge trays 11a, 11b, 11c, 11d Photosensitive drum (corresponding to an image carrier)
13a, 13b, 13c, 13d Scanner (corresponding to image forming means)
15a, 15b, 15c, 15d Primary transfer roller (corresponding to first transfer means)
51 Moisture sensor (equivalent to moisture amount detection means)
52 Temperature / humidity sensor (equivalent to moisture detection means)
61 Recording paper type sensor (equivalent to recording medium type detection means)
100 host computer 200 controller (corresponding to surplus image forming means and image formation selecting means)
P Recording paper (equivalent to recording medium)

Claims (7)

An image forming means for forming an image on the image carrier;
A transfer member for carrying an image formed on the image carrier;
First transfer means for transferring an image formed on the image carrier onto the transfer member;
A second transfer means for transferring the image transferred onto the transfer member to a recording medium;
When forming an image on the image carrier by the image forming unit, an extra image forming unit that forms an extra image that is not transferred onto the recording medium by the second transfer unit on the transfer member;
Have
In an image forming apparatus capable of image formation over the entire area of the recording medium,
The surplus image forming means is configured so that the size of the surplus image area corresponding to the leading end of the recording medium and the size of the surplus image area corresponding to the trailing end of the recording medium are different based on the type of the recording medium. An image forming apparatus for forming an image on the image carrier.   A recording medium type detecting unit for detecting the type of the recording medium, wherein the surplus image forming unit corresponds to a leading image and a trailing edge of the recording medium according to a detection result by the recording medium type detecting unit; The image forming apparatus according to claim 1, wherein the size of the area is determined.   When image formation is performed on the entire area of the recording medium, the surplus image forming means determines the size of the surplus image area corresponding to the rear end of the recording medium as the size of the recording medium capable of continuing image formation. The image forming apparatus according to claim 1, wherein an image is formed on the image carrier so as to be equal to a maximum value of the image. An image forming means for forming an image on the image carrier;
A transfer member for carrying an image formed on the image carrier;
First transfer means for transferring an image formed on the image carrier to the transfer member;
A second transfer means for transferring the image transferred onto the transfer member to a recording medium;
When forming an image on the image carrier by the image forming unit, an extra image forming unit that forms an extra image that is not transferred onto the recording medium by the second transfer unit on the transfer member;
Have
In an image forming apparatus capable of image formation over the entire area of the recording medium,
The surplus image forming unit is configured so that the size of the surplus image area corresponding to the right end of the recording medium and the size of the surplus image area corresponding to the left end of the recording medium are different based on the type of the recording medium. An image forming apparatus for forming an image on an image carrier.   A recording medium type detecting unit configured to detect the type of the recording medium, wherein the surplus image forming unit corresponds to a right end and a left end of the recording medium according to a detection result by the recording medium type detecting unit; The image forming apparatus according to claim 4, wherein the size of the image forming apparatus is determined. An image forming means for forming an image on the image carrier;
A transfer member for carrying an image formed on the image carrier;
First transfer means for transferring an image formed on the image carrier to the transfer member;
A second transfer means for transferring the image transferred onto the transfer member to a recording medium;
When forming an image on the image carrier by the image forming unit, an extra image forming unit that forms an extra image that is not transferred onto the recording medium by the second transfer unit on the transfer member;
Water content detecting means for detecting the water content of the recording medium,
In an image forming apparatus capable of image formation over the entire area of the recording medium,
The surplus image forming means is responsive to the result of detecting the size of the surplus image area corresponding to the leading edge of the recording medium and the size of the surplus image area corresponding to the trailing edge of the recording medium by the moisture amount detecting means. An image forming apparatus for forming an image on the image carrier in a different manner. An image forming means for forming an image on the image carrier;
A transfer member for carrying an image formed on the image carrier;
First transfer means for transferring an image formed on the image carrier to the transfer member;
A second transfer means for transferring the image transferred onto the transfer member to a recording medium;
When forming an image on the image carrier by the image forming unit, an extra image forming unit that forms an extra image that is not transferred onto the recording medium by the second transfer unit on the transfer member;
Water content detecting means for detecting the water content of the recording medium,
In an image forming apparatus capable of image formation over the entire area of the recording medium,
The surplus image forming means is responsive to the result of detecting the size of the surplus image area corresponding to the right end of the recording medium and the size of the surplus image area corresponding to the left end of the recording medium by the moisture amount detecting means. An image forming apparatus for forming an image on the image carrier differently.

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