JP2007212991A - Transfer device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of making both of transferability of a solid portion and that of a halftone portion compatible, and a transfer device to be used for the same. <P>SOLUTION: In the image forming apparatus, an optical writing unit 2 for forming an electrostatic latent image on a photoreceptor drum 11 is capable of making a choice between binary writing control and multivalue writing control, and a transfer unit 6 has a transfer/conveyance belt 60 for applying a bias to a toner image on the photoreceptor and transferring the toner image onto transfer paper 100 and a temperature and humidity detecting means to detect temperature and humidity. When temperature and humidity detection results are those of a set environment, conditions in transfer by the transfer unit are varied according to a method for controlling writing of an electrostatic latent image on the photoreceptor. The set environment is a high temperature and high humidity environment of which the absolute humidity is ≥15 g/m<SP>3</SP>. Conditions in transfer onto the second surface of the transfer paper are made the same in both of the binary writing control and multivalue writing control. The set environment includes a low temperature and low humidity environment of which the absolute humidity is ≤5 g/m<SP>3</SP>, and conditions in transfer onto the second surface of the transfer paper can be varied. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus capable of forming a color image and a transfer device used in the image forming apparatus.

  Representative methods of color image formation include a direct transfer method in which toner images of different colors formed on a plurality of photoconductors are transferred while being superimposed directly on a transfer sheet, and toners of different colors formed on a plurality of photoconductors. There is an intermediate transfer method in which an image is transferred while being superimposed on an intermediate transfer member, and then transferred onto a transfer sheet at once. Since a plurality of photoconductors are arranged side by side facing the transfer paper or intermediate transfer body, this is called a tandem method, and yellow (Y), magenta (M), cyan (C), and black (K) for each photoconductor. For each color, an electrophotographic process such as formation and development of an electrostatic latent image is performed, and the image is transferred onto a running transfer sheet in the direct transfer method, or onto a running intermediate transfer member in the intermediate transfer method.

  In the tandem color image forming apparatus using each of these methods, the direct transfer method receives an endless belt that runs while supporting transfer paper, and the intermediate transfer method receives an image from a photoconductor. Generally, an endless belt to be carried is employed. Then, an image forming unit including four photoconductors is installed side by side on one running side of the belt.

In the tandem color image forming apparatus, it is important to prevent the occurrence of color misregistration by accurately superimposing the toner images of the respective colors.
Japanese Patent Laid-Open No. 2003-21937

  The technique disclosed in Patent Document 1 is a transfer current control device characterized by changing a transfer condition, particularly a transfer current, according to image processing information. However, the optimum transfer condition changes for a halftone image, and the optimum value for a solid image is not changed by image processing. Therefore, if priority is given to the solid transfer property, the optimum place of the transfer current does not depend on the image processing information.

  However, halftones vary depending on the toner image forming method on the image bearing member. In addition, the optimum transfer condition for halftone greatly contributes to temperature and humidity, and the optimum transfer current value for halftone differs only in a specific environment. Therefore, when transferring a halftone toner image in various temperature and humidity environments while ensuring solid transferability, it is desirable to determine the transfer conditions by integrating the environment information and the image processing information.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of solving the above-described conventional problems and achieving both solid and halftone transfer properties and a transfer apparatus used therefor.

  A transfer apparatus according to claim 1 of the present invention is an exposure means for forming an electrostatic latent image on an image carrier, and an exposure means capable of selecting binary write control and multi-value write control, Temperature / humidity detection results in a transfer device used in an image forming apparatus having a transfer unit that applies a bias to a toner image on an image bearing member and transfers the toner image onto a transfer material, and a temperature / humidity detection unit that detects temperature / humidity However, in the case of a set environment, the image forming apparatus includes a control unit that changes transfer conditions by the transfer unit in accordance with a method for controlling writing of the electrostatic latent image on the image carrier.

  That is, the optimum transfer condition (transfer current) for a solid image is different from the optimum transfer condition (transfer current) for a halftone or gray scale image. When emphasizing transferability of a solid image, the transfer current becomes larger than the optimum transfer current for a halftone image (hereinafter, including a grayscale image). For this reason, it is known that a print or white spotted image is generated as a halftone image under the optimum transfer current condition for a solid image in a high temperature / high humidity environment or a low temperature / low humidity environment second side. For this reason, in a high-temperature and high-humidity environment or a low-temperature and low-humidity environment, there may be a transfer condition that does not generate white spots or prints in a halftone image (that is, a condition that the transfer current is insufficient for a solid image). However, the margin of generation of white spots and prints in a halftone image differs depending on the writing method. Therefore, it is necessary to determine the transfer conditions by comprehensively combining the environmental information and the writing control method in order to prevent the occurrence of an abnormal image with halftone while ensuring the transferability of a solid image as much as possible. Therefore, by determining the transfer condition by combining the writing control method and the environment information, it is possible to set the transfer condition so that an abnormal image does not occur in a halftone while ensuring solid transferability. .

The transfer apparatus according to a second aspect of the present invention is the transfer apparatus according to the first aspect, wherein the set environment is a high-temperature and high-humidity environment having an absolute humidity of 15 g / m ³ or more.

  In a high-temperature and high-humidity environment, the moisture content of the transfer paper increases and the paper becomes low-resistance paper. Therefore, the toner charge amount may be reversed due to discharge or charge injection at the transfer nip, and transfer defects or prints may occur. In addition, since the toner charge amount is low in a high humidity environment, the toner charge amount is easily reversed due to discharge or charge injection at the transfer nip portion. Therefore, it is desirable to change the transfer conditions by a writing method in a high humidity environment. Therefore, by changing the transfer conditions by a writing method in a high-humidity environment, it is possible to prevent solid image transfer and halftone abnormal images.

  The transfer device according to claim 3 of the present invention is the transfer device according to claim 2, wherein the transfer condition of the second surface of the transfer material is the same in the binary write control and the multi-value write control. Features.

  The moisture content of the paper decreases as it passes through the fixing. When the moisture content decreases, the paper becomes highly resistant, so that it is difficult to generate halftone prints. For this reason, a large transfer current can be applied to a halftone image. Therefore, on the second surface in a high-humidity environment, a halftone print does not occur even under transfer conditions that can transfer a solid image sufficiently. Therefore, the transfer conditions for the second surface are the same as binary and multivalued, so that the solid transfer property and the halftone transfer property of the second surface can be compatible.

The transfer device according to a fourth aspect of the present invention is the transfer device according to any one of the first to third aspects, wherein the set environment includes a low temperature and low humidity environment having an absolute humidity of 5 g / m ³ or less. The transfer condition of the second surface of the transfer material is changed by a method for controlling the writing of the electrostatic latent image on the image carrier.

  In the second surface of the low temperature and low humidity environment, the paper becomes too high in resistance, and white spots are likely to occur. In particular, white spots tend to occur in multi-valued halftones, so it is desirable to change the transfer conditions depending on the writing method. Therefore, by changing the transfer conditions according to the writing method, it is possible to prevent the occurrence of white spots and ensure the transferability of the solid image.

  The transfer apparatus according to claim 5 of the present invention is the transfer apparatus according to any one of claims 1 to 4, wherein the transfer condition changed according to the writing condition and the environmental condition is a transfer current. . Accordingly, as in the first aspect, it is possible to set the transfer conditions in which an abnormal image does not occur in the halftone while ensuring the solid transfer property.

  The transfer device according to a sixth aspect of the present invention is the transfer device according to any one of the first to fifth aspects, wherein the control means uses different write controls for the copy image and the print image. It is characterized by that.

  The writing method may be different between the copy halftone image and the printer halftone image. In particular, a multi-value writing method is often used for copy images, and halftone abnormal images are likely to occur on the first surface of the high temperature and high humidity environment and the second surface of the low temperature and low humidity environment. For this reason, it is desirable to set different transfer conditions for the copy and the printer. Therefore, by changing the transfer conditions between a copy image and a printer image with different writing methods, it is possible to prevent solid image transfer and halftone abnormal images.

A transfer device according to a seventh aspect of the present invention is the transfer device according to any one of the first to sixth aspects, wherein a maximum toner adhesion amount in a solid image on the transfer material is 0.5 mg / cm ² or less. It is characterized by.

  In recent years, a toner that obtains an image density with a small amount of adhesion may be used for energy saving. However, when an image is formed with a low adhesion amount, it is easily affected by electric discharge at the transfer portion. Therefore, it is possible to achieve both halftone and solid transfer properties for toner used in a low adhesion amount.

  It is important that the toner of the present invention has a specific shape and shape distribution. With an irregularly shaped toner whose shape is too far from a spherical shape, satisfactory transferability and high-quality images free from dust can be obtained. I can't.

  Accordingly, an image forming apparatus according to an eighth aspect of the present invention is an image forming apparatus using the transfer device according to any one of the first to seventh aspects, wherein the average circularity of the toner used is 0.90. It is characterized by being 0.99.

  An image forming apparatus according to a ninth aspect of the present invention is an image forming apparatus using the transfer apparatus according to any one of the first to seventh aspects, wherein the toner has a shape factor SF-1 of 120 to 120. 180, and the shape factor SF-2 is 120 to 190.

  Furthermore, an image forming apparatus according to a tenth aspect of the present invention is the image forming apparatus using the transfer device according to any one of the first to seventh aspects, wherein the toner has a volume average particle diameter Dv (μm) and a number average. A particle diameter Dn (μm) having a Dv / Dn of 1.05 to 1.30 is used.

  In the present invention, by determining the transfer condition by combining the writing control method and the environment information, it is possible to set the transfer condition so that an abnormal image does not occur in the halftone while ensuring the solid transfer property.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

  Hereinafter, the present invention will be described with reference to FIGS. 1 and 2 based on one embodiment applied to an electrophotographic direct color transfer color laser printer (hereinafter referred to as “laser printer”) as an image forming apparatus.

  FIG. 1 is a schematic configuration diagram of a laser printer. This laser printer includes four toner image forming units 1Y, 1M, 1C, 1K (hereinafter referred to as “yellow” (Y), magenta (M), cyan (C), and black (K)). The subscripts Y, M, C, and K of the reference numerals indicate yellow, magenta, cyan, and black members, respectively, and the direction of movement of the transfer paper 100 (the belt 60 along the arrow A in the figure). In the traveling direction) from the upstream side. Each of the toner image forming units 1Y, 1M, 1C, and 1K includes photosensitive drums 11Y, 11M, 11C, and 11K as image carriers and a developing unit. In addition, the arrangement of the toner image forming units 1Y, 1M, 1C, and 1K is set so that the rotation axes of the photosensitive drums are parallel and arranged at a predetermined pitch in the transfer paper moving direction. .

  This laser printer carries the toner image forming units 1Y, 1M, 1C, and 1K, as well as the optical writing unit 2, the paper feed cassettes 3, 4, the resist roller pair 5, and the transfer paper 100, and each toner image forming unit. A transfer unit 6 as a belt driving device having a transfer conveyance belt 60 as a transfer conveyance member that conveys the sheet so as to pass through the transfer position, a belt fixing type fixing unit 7, a paper discharge tray 8, and the like. In addition, a manual feed tray MF and a toner supply container TC are provided, and a waste toner bottle, a duplex / reversing unit, a power supply unit, and the like (not shown) are also provided in a space S indicated by a two-dot chain line. Also provided is temperature / humidity detection means for detecting temperature / humidity.

  The optical writing unit 2 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11K while scanning the laser beam based on the image data. .

FIG. 2 is an enlarged view showing a schematic configuration of the transfer unit 6. The transfer conveyance belt 60 used in the transfer unit 6 is a high-resistance endless single-layer belt having a volume resistivity of 10 ⁹ to 10 ¹¹ Ωcm, and the material thereof is PVDF (polyvinylidene fluoride). The transfer conveyance belt 60 is wound around support rollers 61 to 68 so as to pass through the transfer positions that are in contact with and face the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming units.

  Among these support rollers, the entrance roller 61 on the upstream side in the transfer sheet moving direction is disposed on the outer peripheral surface of the transfer conveyance belt 60 so that the electrostatic adsorption roller 80 to which a predetermined voltage is applied from the power source 65a is opposed. Yes. The transfer paper 100 that has passed between the two rollers 61 and 65 is electrostatically attracted onto the transfer conveyance belt 60.

  A roller 63 is a drive roller that frictionally drives the transfer conveyance belt 60, and is connected to a drive source (not shown) and rotates in the direction of the arrow.

  As a transfer electric field forming means for forming a transfer electric field at each transfer position, transfer bias applying members 67Y, 67M, 67C, and 67K are provided at positions facing the photosensitive drum so as to be in contact with the back surface of the transfer conveyance belt 60. ing. These are bias rollers provided with a sponge or the like on the outer periphery, and a transfer bias is applied to the roller core from each transfer bias power source 9Y, 9M, 9C, 9K. Due to the action of the applied transfer bias, a transfer charge is applied to the transfer conveyance belt 60, and a transfer electric field having a predetermined strength is formed between the transfer conveyance belt 60 and the surface of the photosensitive drum at each transfer position. In addition, a backup roller 68 is provided to keep the contact between the transfer paper and the photoconductor in the area where the transfer is performed, and to obtain the best transfer nip.

  The transfer bias applying members 67Y, 67M, and 67C and the backup roller 68 disposed in the vicinity thereof are integrally held by the swing bracket 93 so as to be rotatable, and can be rotated about a rotation shaft 94. This rotation is clockwise when the cam 96 fixed to the cam shaft 97 is rotated in the direction of the arrow. The entrance roller 61 and the suction roller 80 are integrally supported by the entrance roller bracket 90, and can be rotated clockwise from the state of FIG. A hole 95 provided in the swing bracket 93 and a pin 92 fixed to the entrance roller bracket 90 are engaged with each other, and rotate in conjunction with the rotation of the swing bracket 93. By the clockwise rotation of these brackets 90, 93, the bias applying members 67Y, 67M, 67C and the backup roller 68 disposed in the vicinity thereof are separated from the photoreceptors 11Y, 11M, 11C, and the entrance roller 61 and the suction roller 80 also moves downward. It is possible to avoid contact between the photoconductors 11Y, 11M, and 11C and the transfer conveyance belt 60 when forming a black-only image.

  On the other hand, the transfer bias applying member 67K and the backup roller 68 adjacent to the transfer bias applying member 67K are rotatably supported by the outlet bracket 98, and are rotatable about a shaft 99 coaxial with the outlet roller 62. When attaching / detaching the transfer unit 6 to / from the main body, the transfer unit 6K is rotated clockwise by operating a handle (not shown), and the transfer bias applying member 67K and the backup roller 68 adjacent thereto are moved from the black image forming photosensitive member 11K. They are separated.

  A cleaning device 85 composed of a brush roller and a cleaning blade is disposed on the outer peripheral surface of the transfer conveyance belt 60 wound around the driving roller 63. The cleaning device 85 removes foreign matters such as toner adhering to the transfer conveyance belt 60.

  A roller 64 is provided downstream of the drive roller 63 in the traveling direction of the transfer conveyance belt 60 in a direction to push the outer peripheral surface of the transfer conveyance belt, and a winding angle around the drive roller 83 is ensured. A tension roller 65 that applies tension to the belt with a pressing member (spring) 69 is provided in the loop of the transfer conveyance belt 60 further downstream from the roller 64.

  Note that the alternate long and short dash line in FIG. 1 indicates the conveyance path of the transfer paper 100. The transfer paper 100 fed from the paper feed cassettes 3 and 4 or the manual feed tray MF is transported by transport rollers while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration roller pair 5 is provided. The transfer paper 100 delivered at a predetermined timing by the registration roller pair 5 is carried on the transfer conveyance belt 60, conveyed toward the toner image forming units 1Y, 1M, 1C, and 1K, and passes through the transfer nips. .

  The toner images developed on the toner drums 11Y, 11M, 11C, and 11K of the toner image forming units 1Y, 1M, 1C, and 1K are superimposed on the transfer paper 100 at the transfer nips, respectively. It is transferred onto the transfer paper 100 under the action of pressure. By this superposition transfer, a full-color toner image is formed on the transfer paper 100.

  The surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K after the toner image transfer are cleaned by a cleaning device, and are further discharged to prepare for the formation of the next electrostatic latent image.

  On the other hand, the transfer paper 100 on which the full-color toner image is formed is fixed in the first paper discharge direction B or the second in accordance with the rotation posture of the switching guide G after the full-color toner image is fixed by the fixing unit 7. In the paper discharge direction C. When the paper is discharged from the first paper discharge direction B onto the paper discharge tray 8, it is stacked in a so-called face-down state with the image surface down. On the other hand, when the paper is discharged in the second paper discharge direction C, it is conveyed toward another post-processing device (such as a sorter or a binding device) (not shown), or is registered again for double-sided printing via a switchback unit. It is conveyed to the roller pair 5.

FIG. 3 shows a comparison of the transferability between the binary writing on the first surface and the multi-valued writing image on the transfer paper 100 in a high-temperature and high-humidity environment with an absolute humidity of 15 g / m ³ or more. In FIG. 3, the horizontal axis represents the transfer current (μA), and the vertical axis represents the image density. The image density was a monochromatic image density measured by a reflection fluorescent color density meter 938.

  As a result, the transferability of the solid image is almost the same for both binary writing and multi-value writing. However, with regard to halftone images, in the case of multi-level writing, image density decreases when the transfer current is increased. In addition, the density of the halftone image has already been lowered at around 14 μA, which is considered to have sufficient solid transfer property of the multi-value writing method. In order to achieve both halftone and solid images in the multi-value writing method, the transfer current is preferably set to 7 to 10 μA. However, in binary writing, the density of the halftone image does not decrease even when the transfer current is increased. For this reason, it is considered desirable to set the solid image to 10 to 15 μA that can sufficiently ensure the transferability of the solid image.

FIG. 4 shows a comparison of the transferability between the binary writing on the first surface and the multi-level writing image in the high temperature and high humidity environment. In FIG. 4 as well, the horizontal axis represents the transfer current (μA), and the vertical axis represents the image density. The optimum transfer current value for a solid image is substantially the same value (around 14 μA in FIG. 4) regardless of the writing method. However, regarding the occurrence of white spots, the multi-value writing halftone is generated with a lower transfer current (transfer bias). Therefore, depending on the writing method, the optimum value of the transfer condition on the second surface differs in a low-temperature and low-humidity environment where the absolute humidity is 5 g / m ³ or less, and the multi-value is about 10 μA, and the binary value is 12 to 14 μA.

  FIG. 5A conceptually shows the photoreceptor surface potential of the solid portion and the halftone portion (in the case of multi-level writing control). The solid portion is exposed so that the potential after exposure is close to 0 V in both binary writing and multi-value writing. Therefore, there is no difference in the photosensitive charge position of the solid portion, whether binary or multivalued. The most different point between binary writing and multi-value writing is halftone writing. When a halftone is expressed by binary values, the halftone is expressed by reducing the exposure area without changing the exposure intensity for each dot. That is, if the area to be exposed is small, it becomes a thin halftone, and if the area to be exposed is large, it becomes a halftone close to solid. However, in the case of multilevel writing, a method for controlling the exposure intensity is used in addition to the binary halftone expression method. FIG. 5B shows the surface potential of the photoconductor of the multilevel writing method. In the multi-value method, control is performed so that the potential after exposure is different from the exposure potential of the solid portion. Therefore, the halftone expression method is wider than binary writing, leading to high image quality. Since a copy image may be compared with an original, multi-level writing is often employed to faithfully copy the original.

  FIG. 6 shows the range distribution of environmental control. The horizontal axis is relative humidity (% RH), and the vertical axis is temperature (° C.). When creating an image, the temperature and humidity environment around the imaging area is detected, and if the environmental conditions are a high-temperature, high-humidity environment or a low-temperature, low-humidity environment, control is performed to use different transfer conditions for binary writing and multi-value writing. To do.

  In the above embodiment, the present invention is applied to the transfer unit 6 in the tandem printer in which a plurality of photosensitive drums 11Y, 11M, 11C, and 11K are arranged on the transfer conveyance belt 60. However, the present invention is applied. Possible printers and belt drives are not limited to this configuration. The present invention can be applied to any belt driving device in a printer having a belt driving device that rotationally drives an endless belt stretched around a plurality of rollers by at least one of the rollers.

  The toner used in the image forming apparatus according to the present invention will be described.

(Circularity and circularity distribution)
As already mentioned, it is important that the toner in the present invention has a specific shape and shape distribution, and in the case of an irregularly shaped toner having an average circularity of less than 0.90 and far away from a sphere, Satisfactory transfer and high-quality images without dust cannot be obtained. As a method for measuring the shape, an optical detection band method is suitable in which a suspension containing particles is passed through an imaging unit detection band on a flat plate, and a particle image is optically detected and analyzed by a CCD camera. Toner having an average circularity of 0.90 to 0.99, which is a value obtained by dividing the perimeter of an equivalent circle having the same projected area obtained by this method by the perimeter of the actual particle, has high reproducibility with an appropriate density reproducibility. It was found to be effective for forming a clear image. More preferably, particles having an average circularity of 0.93 to 0.97 and a circularity of less than 0.94 are 10% or less. In addition, when the average circularity exceeds 0.99, in a system employing blade cleaning or the like, a cleaning failure occurs on the photosensitive member or the transfer belt, causing stains on the image. For example, when outputting an image with a low image area ratio, there is little transfer residual toner and there is no problem with poor cleaning. However, when outputting an image with a high image area ratio such as a color photographic image, If an untransferred image remains on the photoreceptor due to a defect or the like, a cleaning defect is likely to occur. If the above-mentioned cleaning failures occur frequently, further, the charging roller that contacts and charges the photoreceptor is contaminated, and the original charging ability cannot be exhibited.

(Measurement method of circularity)
The average circularity can be measured by a flow type particle image analyzer FPIA-2100 (manufactured by Toa Medical Electronics Co., Ltd.). As a specific measuring method, 0.1 to 0.5 ml of a surfactant, preferably alkylbenzene sulfonate is added as a dispersant to 100 to 150 ml of water from which impure solids have been removed in advance, and further measurement is performed. Add about 0.1-0.5g of sample. The suspension in which the sample is dispersed is obtained by performing dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and measuring the shape and distribution of the toner with the above apparatus at a dispersion concentration of 3000 to 10,000 / μl. .

(Dv / Dn)
The ratio of the volume average particle diameter Dv to the number average particle diameter Dn is such that the volume average particle diameter (Dv) of the toner is 4 to 8 μm, and the ratio (Dv / Dn) to the number average particle diameter (Dn) is 1. According to the dry toner of 05 to 1.30, preferably 1.10 to 1.25, the particle size distribution of the toner becomes narrow, and the following advantages are generated.
(1) Since a phenomenon such as selective development on the toner particle size surface (toner particles having a (suitable) toner particle size corresponding to the image pattern are selectively developed) is unlikely to occur, a stable image can be always obtained. Can be formed.
(2) When a toner recycling system is installed, small-sized toner particles that are difficult to transfer are recycled in a large quantity, but since the toner particle size distribution is originally narrow, it is difficult to receive the above-described action. This also makes it possible to always form a stable image.
(3) In the two-component developer, even if the toner balance for a long time is performed, the fluctuation of the toner particle diameter in the developer is reduced, and good and stable developability can be obtained even in the long-term stirring in the developing device. can get.
(4) Even when used as a one-component developer, even if the balance of the toner is performed, the fluctuation of the toner particle diameter is reduced, the toner is filmed on the developing roller, and the toner is thinned. Therefore, the toner is not fused to a member such as a blade, and good and stable developability and image can be obtained even when the developing device is used (stirred) for a long time.

  In general, it is said that the smaller the particle size of the toner, the more advantageous it is to obtain a high-resolution and high-quality image, but it is disadvantageous for transferability and cleaning properties. is there. Further, when the volume average particle diameter is smaller than the range described in the present embodiment, in the two-component developer, the toner is fused to the surface of the carrier in the long-term stirring in the developing device, and the charging ability of the carrier is reduced. When used as a one-component developer, toner filming on the developing roller and toner fusion to a member such as a blade for thinning the toner are likely to occur. Further, these phenomena are the same for the toner having a fine powder content larger than the range of the present invention.

  Conversely, when the toner particle diameter is larger than the range shown in the present embodiment, it becomes difficult to obtain a high-resolution and high-quality image and the balance of the toner in the developer is performed. In many cases, the fluctuation of the particle diameter of the toner becomes large. It was also clarified that the same applies when the volume average particle diameter / number average particle diameter is larger than 1.30.

  Further, when Dv / Dn (volume average particle diameter / number average particle diameter) is smaller than 1.05, there are preferable aspects from the viewpoint of stabilizing the behavior of the toner and equalizing the charge amount, but the thin line portion is Since it becomes difficult to separate the functions depending on the toner particle size, such as development with small-sized particles, while developing a solid image mainly with large-sized particles, it is not preferable.

(Measurement method for toner particle size)
Examples of the measuring device for the particle size distribution of toner particles by the Coulter counter method include Coulter Counter TA-II and Coulter Multisizer II (both manufactured by Coulter). The measurement method is described below.

  First, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of an aqueous electrolytic solution. Here, the electrolytic solution is prepared by preparing an about 1% NaCl aqueous solution using primary sodium chloride, and for example, ISOTON-II (manufactured by Coulter) can be used. Here, 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the measurement device is used to measure the volume and number of toner particles or toner using a 100 μm aperture as an aperture. Volume distribution and number distribution are calculated. From the obtained distribution, the volume average particle diameter (Dv) and the number average particle diameter (Dn) of the toner can be obtained.

  As channels, 2.00 to less than 2.52 μm; 2.52 to less than 3.17 μm; 3.17 to less than 4.00 μm; 4.00 to less than 5.04 μm; 5.04 to less than 6.35 μm; 6 Less than 35 to 8.00 μm; less than 8.00 to less than 10.08 μm; less than 10.08 to less than 12.70 μm; less than 12.70 to less than 16.00 μm; less than 16.00 to less than 20.20 μm; Uses 13 channels of less than 40 μm; 25.40 to less than 32.00 μm; 32.00 to less than 40.30 μm, and targets particles having a particle size of 2.00 μm to less than 40.30 μm.

(Shape factors SF-1 and SF-2)
As shown in FIG. 7, the shape factor SF-1 here is a value indicating the ratio of the roundness of the shape of the spherical substance, and is the maximum of the elliptical figure formed by projecting the spherical substance on a two-dimensional plane. It is represented by a value obtained by dividing the square of the length MXLNG by the graphic area AREA and multiplying by 100π / 4. That is, the shape factor SF-1 is
SF-1 = {(MXLNG) 2 / AREA} × (100π / 4)
It is defined as When the value of SF-1 is 100, the shape of the substance becomes a true sphere, and as the value of SF-1 increases, the shape of the substance becomes indefinite. Further, as shown in FIG. 8, the shape factor SF-2 is a numerical value indicating the ratio of the unevenness of the shape of the substance, and the square of the perimeter PERI of the figure formed by projecting the substance on the two-dimensional plane is the figure area. It is expressed as a value when divided by AREA and multiplied by 100 / 4π. That is, the shape factor SF-2 is
SF-2 = {(PERI) 2 / AREA} × (100 / 4π)
It is defined as When the value of SF-2 is 100, there is no unevenness on the surface of the substance, and as the value of SF-2 increases, the unevenness on the surface of the substance becomes more prominent.

  In this embodiment, the shape factors SF-1 and SF-2 are randomly sampled 100 times using a FE-SEM (S-800) manufactured by Hitachi, Ltd., and the image information is obtained from an image manufactured by Nireco. The sample was introduced into an analyzer (LUSEX 3) for analysis, and calculated from the above formula.

  It has been clarified by the present inventors that the transfer efficiency increases when the toner shape approaches the spherical shape as much as possible (both SF-1 and SF-2 approach 100). This is because there is only a point contact between the toner particles and the thing (toner particles, image carrier, etc.) in contact with the toner particles due to the shape effect, so that the toner fluidity is increased or the toner is adsorbed on the image carrier, etc. This is thought to be because the force (mirror power) is weakened and is easily affected by the transfer electric field.

  On the other hand, when the shape of the toner approaches a spherical shape, it is disadvantageous for mechanical cleaning (such as blade cleaning). As described above, this is because the toner fluidity is increased and the adsorbing force (mirroring force) on the image carrier is weakened so that the toner can easily pass through the slight gap between the cleaning member and the image carrier. End up. Therefore, from the viewpoint of cleaning properties, the shape of the toner is somewhat irregular (in the direction in which the value of SF-1 is greater than 100) or uneven (in the direction in which the value of SF-2 is greater than 100). It is more preferable.

1 is a schematic configuration diagram of a laser printer that is an example of an image forming apparatus according to an embodiment of the present disclosure. 1 is an enlarged view showing a schematic configuration of a transfer unit of the laser printer of FIG. Diagram showing difference in transferability between binary writing and multi-value writing (first surface of high temperature and high humidity environment) Diagram showing difference in transferability between binary writing and multi-value writing (second surface in low temperature and low humidity environment) Diagram showing the photoreceptor potential in the solid and halftone parts Diagram showing environmental control range Diagram showing shape factor SF1 Diagram showing shape factor SF2

Explanation of symbols

1Y, 1M, 1C, 1K: toner image forming unit 2: optical writing unit 3, 4: paper feeding cassette 5: registration roller pair 6: transfer unit 7: fixing unit 8: paper discharge tray 9: transfer bias power supply 10: photosensitive Body unit 11Y, 11M, 11C, 11K: Photoconductor drum 60: Transfer conveyance belt 61-68: Support roller 80: Electrostatic adsorption roller 80a: Power supply 90: Entrance roller bracket 91: Shaft 92: Pin 93: Swing bracket 94 : Rotating shaft 95: hole 96: cam 97: cam shaft 98: outlet bracket 99: shaft 100: transfer paper A: belt running direction B: first paper discharge direction C: second paper discharge direction S: space MF : Manual feed tray G: Switching guide

Claims (10)

Exposure means for forming an electrostatic latent image on an image carrier, exposure means capable of selecting binary writing control and multi-value writing control;
Transfer means for applying a bias to the toner image on the image carrier and transferring it onto a transfer material;
In a transfer device used for an image forming apparatus having a temperature / humidity detecting means for detecting temperature / humidity,
When temperature and humidity detection results are in a set environment, the image forming apparatus includes a control unit that changes a transfer condition by the transfer unit in accordance with a method for controlling the writing of an electrostatic latent image on the image carrier. Transfer device. The transfer apparatus according to claim 1, wherein the set environment is a high-temperature and high-humidity environment having an absolute humidity of 15 g / m ³ or more. 3. The transfer apparatus according to claim 2, wherein the transfer condition of the second surface of the transfer material is the same in the binary write control and the multi-value write control. 4. The transfer apparatus according to claim 1, wherein the set environment includes a low-temperature and low-humidity environment having an absolute humidity of 5% or less, and an electrostatic latent image writing control method on the image carrier. To change the transfer condition of the second surface of the transfer material. 5. The transfer apparatus according to claim 1, wherein the transfer condition changed according to the writing condition and the environmental condition is a transfer current. 6. The transfer apparatus according to claim 1, wherein the control unit uses different write controls for the copy image and the print image. 7. The transfer device according to claim 1, wherein the maximum toner adhesion amount in the solid image on the transfer material is 0.5 mg / cm < ² > or less. 8. An image forming apparatus using the transfer device according to claim 1, wherein an average circularity of toner used is 0.90 to 0.99. 8. The image forming apparatus using the transfer device according to claim 1, wherein the toner has a shape factor SF-1 of 120 to 180 and a shape factor SF-2 of 120 to 190. An image forming apparatus. 8. The image forming apparatus using the transfer device according to claim 1, wherein a volume average particle diameter Dv (μm) and a number average particle diameter Dn (μm) of the toner have a Dv / Dn of 1.05. An image forming apparatus using an image forming apparatus having a value of ˜1.30.