JP2015108784A - Two-component developer forming method, image forming apparatus, and developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for making appropriate the amount of toner charged with an appropriate charge amount in order to always form an excellent image even when the use environment is changed, and to provide an image forming apparatus and a developer.SOLUTION: Two kinds of first carrier C1 having an average charge amount of 23 μC/g and a second carrier C2 having an average charge amount of 41 μC/g are mixed with toner to give a developer D. The appropriate charge amount for development of the developer D is in the vicinity of 30 μC/g. The appropriate amount of the toner is present in the center of the distribution of charge amounts of the toner at an ordinary temperature and humidity of 25°C and 50%. In the environment of a low temperature and humidity of 10°C and 20%, the distribution of charge amounts of the toner moves toward the direction of a high charge amount, but the amount of the toner for the appropriate charge amount is appropriately kept. In the environment of a high temperature and humidity of 30°C and 80%, the distribution of charge amounts of the toner moves toward the direction of a low charge amount, but the amount of the toner for the appropriate charge amount is appropriately kept.

Description

  The present invention relates to a two-component developer forming method, an image forming apparatus, and a developer used in electrophotographic image forming such as copying machines, printers, and facsimiles.

  Conventionally, there is an electrophotographic image forming apparatus. In this image forming apparatus, generally, a photosensitive drum is uniformly charged and initialized, an electrostatic latent image is formed on the photosensitive drum by optical writing, and the electrostatic latent image is converted into a toner image. Is directly or indirectly transferred onto a transfer material such as paper and fixed by a fixing device.

  Such electrophotographic image forming apparatuses include those using a one-component developer composed only of toner and those using a two-component developer composed of toner and carrier. In recent years, a method using a two-component developer can cope better with the demand for high-speed printing (hereinafter also referred to as printing) processing.

  The carrier composed of the magnetic particles of the two-component developer is mixed and stirred with the toner in the developing device to give the toner a predetermined triboelectric charge. The charged toner temporarily adheres to the surface of the carrier and coats the surface of the carrier.

  The carrier adhering to the magnetic developing roller carries charged toner onto the photosensitive member, transfers the toner to the electrostatic latent image on the photosensitive member, and develops the toner image on the electrostatic latent image.

  The carrier from which the toner on the surface has been released remains on the developing roller, and is mixed and stirred again with new toner that is returned to the developing device and replenished to the developing device, and the toner is triboelectrically charged. It is used repeatedly, such as carrying.

  Toner is supplied to the developing device from a toner supply device. As a toner replenishment path from the toner supply device to the developing device, a pipe having a built-in coil screw or a replenishment path using a natural fall path due to the gravity of the toner is used.

  Here, if the toner concentration in the developer of the developing device is too high, background staining or the like occurs. Conversely, if the toner density is too low, a high density image cannot be obtained. Therefore, in order to obtain a high-quality image, it is necessary to control the toner concentration of the developer in the developing device supplied to the toner image carrier within a certain range.

  Therefore, a developing device of an electrophotographic image forming apparatus that forms an image using such a developer is provided with a toner density sensor for measuring the amount of toner consumed by printing. When it is detected that the toner density is lower than a predetermined value, the developing device is replenished with toner.

  Generally, a magnetic sensor that detects magnetic permeability is used as the toner concentration sensor. The toner concentration sensor exposes a detection surface to a part of the inner wall surface of the developing device, and detects a change in magnetic permeability from a carrier in the developer around the detection surface. That is, when the toner concentration is high, the magnetic permeability decreases and the sensor output becomes weak. When the toner concentration is low, the magnetic permeability increases and the sensor output becomes strong.

  When the sensor output exceeds the replenishment reference voltage value (replenishment voltage threshold), the toner is replenished by a shortage, and when the output falls below the reference voltage value, the replenishment is stopped. The amount of toner at this time is preferably supplied in a fixed amount per replenished time.

  Concerning toner density control, appropriate developer agitation is performed according to the amount of toner replenishment, the toner charge amount is made constant, thereby suppressing image density reduction and early deterioration of the developer due to over-stirring of the developer, There has been proposed a two-component developing device that reduces toner scattering and background fogging due to insufficient stirring, and further accurately detects the toner concentration in the developer and performs stable toner concentration control. (For example, see Patent Document 1.)

  By the way, it does not mean that the charge amount of toner should be high. If it is too high, the development is completed with a small amount of toner, resulting in a low image density. Conversely, if the charge amount of the toner is too low, a large amount of toner adheres to the photosensitive drum, resulting in an excessive image density, which impairs the reproducibility of the image. Therefore, it is necessary to make the toner charge amount constant as described in Patent Document 1.

  Therefore, in Patent Document 1, two control units are provided, one of which controls the rotation speed of the agitation roller that agitates the replenished toner with the existing developer at a low speed and a high speed according to the toner replenishment amount, and the other develops. The rotational speed of the spiral roller that conveys the developer to the sensor is switched between high speed and low speed so that the developer is supplied to the developing tank provided with the toner concentration sensor at a substantially constant density.

  In addition to the above, methods for controlling the charge amount of the toner to an appropriate value include adding a charge control agent to the toner or coating the surface of the carrier with a resin. However, this alone is not applicable to changes in environmental temperature and humidity.

  Therefore, a detector for detecting the amount of toner developed on the photosensitive member or transferred to the transfer belt is provided, and the developing bias is controlled based on the detected value to adhere to the photosensitive member. Methods such as controlling the amount of toner have been put into practical use.

JP 05-006090 A

  However, as in Patent Document 1, it is cumbersome and requires advanced control logic to control the rotation speed of the stirring roller and the rotation speed of the spiral roller individually and at high speed and low speed by two control units. It is not easy to realize.

  In addition, a method of changing the developing bias that has been put into practical use is, for example, a problem of carrier pulling when the developing bias is increased to ensure the image density when the toner charge amount increases and the image density decreases in a low humidity environment. Will occur.

  Therefore, it is necessary to increase the initialization potential of the photosensitive member as the developing bias is increased. However, when the initialization potential of the photosensitive member is increased, the exposure portion potential is also increased. Therefore, it is necessary to perform complicated control that the light quantity of the optical writing head has to be increased in order to lower the exposure portion potential.

  The present invention solves the above-described conventional problems, and it is always good even if the usage environment fluctuates by simply changing the configuration of the developer without fluctuating the number of rotations of the member and the bias output value. It is an object of the present invention to provide a two-component developer forming method, an image forming apparatus, and a developer that optimize toner charge distribution suitable for developing an image.

  In order to solve the above problems, the two-component developer forming method of the present invention has a toner amount of a first charge amount per unit weight of a toner and a mixture obtained by mixing the toner alone with the toner. The toner amount of the second charge amount different from the first charge amount per unit weight of the first carrier that is the largest and the mixture obtained by mixing with the toner alone is the largest. A two-component developer is formed by mixing the second carrier.

  The present invention relates to a two-component developer forming method and an image forming apparatus that optimizes a toner charge distribution suitable for development that always creates a good image even if the use environment changes, by simply changing the configuration of the developer. As well as a developer.

1 is a cross-sectional view illustrating an internal configuration of a full-color image forming apparatus (printer) according to Embodiment 1 of the invention. (a), (b) is an expanded sectional view which shows the developing device of the printer based on Example 1 with a photosensitive drum. FIG. 3 is a cross-sectional view illustrating an internal configuration and a developer reflux path by cutting the developing device of the printer according to the first embodiment in a direction indicated by an arrow g in FIG. 1 is a circuit block diagram including a printer control device according to Embodiment 1. FIG. FIG. 7 is a diagram illustrating a result of measuring a toner charge amount distribution in a two-component developer similar to a normal one. (a), (b), (c) is a diagram showing the distribution of the charge amount in each environment of the developer composed of the two-type mixed carrier and toner of the present invention.

Hereinafter, in describing embodiments of the present invention, definitions of important concepts and terms are given.
The flying type charge amount measuring device is a metal cylinder having a magnet arranged inside, and an electric field generated between the metal cylinders arranged on the outer periphery of the metal cylinder, and the developer placed on the inner cylinder is placed on the outer cylinder. This is a measuring apparatus that can measure the amount of charge of toner adhered to the outside by flying to the outside.
Normal temperature and humidity are defined in the Japanese Industrial Standards as normal temperature = 5 to 35 ° C and normal humidity = 45 to 85%, but as an office environment in which the image forming apparatus in the present invention is generally used, Normal temperature = 15 to 25 ° C., normal humidity = 45 to 60%. According to the Japanese Pharmacopoeia, the normal temperature for pharmaceuticals and the like may be 15 to 25 ° C. In the present invention, normal temperature = It is defined as 15 to 25 ° C. and normal humidity = 45 to 60%. In the description of room temperature and normal humidity, low temperature and low humidity, and high temperature and high humidity in the following examples, the actual values at the time of measurement are clearly described without providing a range of values. That is, normal temperature and normal humidity (25 ° C./50%), low temperature / low humidity (10 ° C./20%), and high temperature / high humidity (30 ° C./80%).
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Example 1]

  FIG. 1 is a cross-sectional view illustrating an internal configuration of a full-color image forming apparatus (hereinafter simply referred to as a printer) according to Embodiment 1 of the present invention.

  An image forming apparatus 1 shown in FIG. 1 is an electrophotographic secondary transfer tandem color image forming apparatus, and includes an image forming unit 2, a transfer belt unit 3, a toner supply unit 4, a paper feeding unit 5, and a belt. It is composed of a type fixing unit 6.

  The image forming unit 2 is in contact with the lower running unit surface 8a of the transfer belt 8 of the transfer belt unit 3 and multi-stages four developing devices 9 (9y, 9m, 9c, 9k) from right to left in FIG. It consists of a side-by-side configuration. The image forming unit 2 is held by a frame of the main body of the image forming apparatus 1 so that it can be moved up and down from the printing execution position shown in FIG. 1 to a maintenance position below it.

  Of the four developing devices 9, three developing devices 9y, 9m, and 9c on the downstream side (right side in the figure) are yellow (Y), magenta (M), and cyan (C), which are subtractive three primary colors, respectively. A mono-color image is formed with the color toner, and the developing device 9k forms a monochrome image mainly with black (K) toner used for characters and dark portions of the image.

  Each of the developing devices 9 has the same configuration except for the color of the toner that develops the image. Therefore, the configuration of the developing device 9k for black (K) toner will be described below as an example.

  The developing device 9 includes a photosensitive drum 10 at the top. The photosensitive drum 10 has a peripheral surface made of, for example, an organic photoconductive material. A cleaning blade 11, a charging roller 12, an optical writing head 13, and a developing roller 15 of the developing device 14 are arranged around the periphery of the photosensitive drum 10.

  The developing device 14 includes a first stirring / conveying member 16 and a second stirring / conveying member 17 in two developing tanks located below the developing roller 15. Details of the first and second stirring and conveying members 16 and 17 will be described later.

  The transfer belt unit 3 has an endless transfer belt 8 that extends in the shape of a flat loop in the left-right direction in the figure at approximately the center of the main unit, and the transfer belt 8 is stretched over the transfer belt 8. A driving roller 18 and a driven roller 19 are provided to circulate and move counterclockwise as indicated by arrows a and b in the figure.

  The above-described transfer belt 8 is directly transferred to the surface of the belt that circulates below by a primary transfer roller 21 that is integrated with the unit and pressed against the photosensitive drum 10 via the transfer belt 8 (primary transfer). Then, the toner image is conveyed to the secondary transfer unit 23 to the paper for further transfer (secondary transfer) to the paper.

  In the transfer belt unit 3, the cleaning blade 25 of the belt cleaner 24 is disposed in contact with the surface of the belt 18 that is stretched around the driving roller 18. A waste toner collecting container 26 is detachably disposed below the belt cleaner 24.

  In the belt cleaner 24, the cleaning blade 25 abuts on the surface of the transfer belt 8 to scrape and remove the waste toner, and the waste toner is sent to a lower waste toner collection container 26 by a conveying member.

  The toner supply unit 4 includes four toner hoppers 27 (27y, 27m, 27c, and 27k) disposed above the upper running unit of the transfer belt 8. The four toner hoppers 27y, 27m, 27c, and 27k contain yellow (Y), magenta (M), cyan (C), and black (K) toners, respectively.

  The toner supply unit 4 includes yellow (Y), magenta (M), cyan (C), and black (Y) as indicated by Y, M, C, and K (hereinafter referred to as “YMCK”) in FIG. One of the toners K) is supplied to the developing device 14 of the developing device 9 through a toner supply path (not shown).

  The paper feed unit 5 includes one paper feed cassette 29. A large number of sheets 30 are stored in the sheet feeding cassette 29. A paper take-out roller 31, a feed roller 32, a separating roller 33, and a standby conveyance roller pair 34 are disposed in the vicinity of the paper feed port (right side of the drawing) of the paper feed cassette 29.

  In the paper conveyance direction (vertical upward direction in the figure) of the standby conveyance roller pair 34, a secondary transfer roller 35 that is in pressure contact with the driven roller 19 via the transfer belt 8 is disposed, and the secondary transfer roller 35 to the above-described paper 30 is provided. A transfer portion 23 is formed.

  A diffuse reflection type density sensor 36 is disposed in the vicinity of the lower running portion surface 8a of the transfer belt 8 at a substantially intermediate position between the secondary transfer portion 23 and the most downstream developing device 9y. A belt-type heat fixing unit 6 is disposed downstream (upward in the drawing) of the secondary transfer portion.

  Further downstream of the belt-type heat fixing unit 6, a pair of unillustrated unloading rollers for unloading the fixed sheet from the belt-type heat fixing unit 6 and a sheet discharge tray on which the unloaded paper is formed on the upper surface of the apparatus. A pair of paper discharge rollers (not shown) for discharging paper to 37 is disposed. An operation panel unit 38 is disposed at an upper end of the main body located to the right of the paper discharge tray 37 with a slight inclination.

  FIGS. 2A and 2B are enlarged sectional views showing the developing unit 14 together with the photosensitive drum 10. As shown in FIG. 2A, the developing device 14 includes two developing tanks 43 (43 a and 43 b) partitioned by an outer wall frame 41 and an inner partition wall 42.

  In the upper first developing tank 43a, the developing roller 15 and the first stirring / conveying member 16 described above are arranged. A doctor blade 44 is in contact with the developing roller 15. The second stirring / conveying member 17 described above is disposed in the lower second developing tank 43b. In the developing tank 43b, a toner density sensor 45 is arranged with its detection surface 46 exposed in the tank.

  The first stirring / conveying member 16 includes a rotating shaft 47 and a helical fin 48 fixed to the rotating shaft 47 in a spiral shape. The second stirring / conveying member 17 includes a rotation shaft 49 and a helical fin 51 fixed to the rotation shaft 49 in a spiral shape.

  If the toner density of the developer is less than the specified level, the toner density sensor 45 detects a decrease in toner density. When a decrease in toner density is detected, toner is supplied from a toner hopper 27 corresponding to the developing device 14 of the toner supply unit 4 through a supply port described later.

  Since the detection surface 46 of the toner density sensor 45 is exposed in the tank, the developer tends to stay on the detection surface 46. If the developer stays on the detection surface 46, the detection accuracy of the toner density sensor 45 is lowered.

  In order to prevent the detection accuracy of the toner density sensor 45 from being lowered, the rotation shaft 49 of the second agitating / conveying member 17 in the developing tank 43b is positioned so as to face the detection surface 46 of the toner density sensor 45. Further, a cleaning blade 54 comprising a blade holding portion 52 and an elastic sheet (blade) 53 held by the blade holding portion 52 is fixed.

  The cleaning blade 54 rotates together with the rotating shaft 49 of the stirring and conveying member 17, and rubs the detection surface 46 of the toner density sensor 45 with the elastic sheet 53 as shown in FIG. The developer to be retained is removed and replaced with the developer conveyed immediately thereafter. This prevents erroneous detection of the toner concentration that may be caused by the developer staying on the detection surface 46 of the toner concentration sensor 45.

  FIG. 3 is a cross-sectional view showing the internal structure and the developer reflux path by cutting the developing device 14 in the direction indicated by the arrow g in FIG. In FIG. 3, the same components as those shown in FIGS. 2A and 2B are denoted by the same reference numerals as those shown in FIGS. In FIG. 3, the cleaning blade 54 is not shown.

  As shown in FIG. 3, both end portions of the developing roller 15 are rotatably supported by the developing roller support portions 41 a and 41 b of the outer wall frame 41 of the developing device 14 via the rotation shaft 55. One end (left side in FIG. 3) of the rotation shaft 55 is formed to extend further than the developing roller support 41b, and is provided with a gear 56 at the tip.

  The outer wall frame 41 of the developing device 14 extends to the left in the same manner as the rotation shaft 55 of the developing roller 15 extends further than the developing roller support portion 41b to form an extended outer wall frame 41c. doing.

  A first circulation port 57 is formed inside the frame formed by the extended outer wall frame 41c. A toner supply port 58 is connected below the first circulation port 57 of the developing tank 43b.

  When a decrease in toner density is detected by the toner density sensor 45, toner is supplied from the toner hopper 27 of the toner supply unit 4 corresponding to the developing device 14 through the toner supply port 58.

  The rotary shaft 47 of the first agitating and conveying member 16 has one end rotatably supported by the outer wall frame 41 on the same side as the developing roller support portion 41a and the other end supported by the extended outer wall frame 41c. It is rotatably supported.

  A drive relay gear 59 is fixed to the outer end portion 47a that protrudes outside the extended outer wall frame 41c of the rotary shaft 47 of the first agitating and conveying member 16. In addition, an external engagement gear 61 and a drive transmission gear 62 are fixed to an external shaft 49 a that protrudes outside the extended outer wall frame 41 c of the rotation shaft 49 of the second agitating and conveying member 17.

  The drive transmission gear 62 rotates by engaging with a drive gear 65 of a developing device rotation device 66 composed of a motor 63 on the printer 1 main unit side, a rotation shaft 64 thereof, and a drive gear 65 fixed to the tip thereof. Then, the second agitation transport member 17 is rotated and the external engagement gear 61 is rotated.

  The external engagement gear 61 meshes with the drive relay gear 59 of the rotary shaft 47 of the first agitation transport member 16 and transmits the rotational drive to the drive relay gear 59. The drive relay gear 59 rotates the first agitation transport member 16 and relays the rotational drive from the external engagement gear 61 to the gear 56. The gear 56 rotates the developing roller 15.

  3 and 2 (a), the first stirring and conveying member 16 rotates counterclockwise in FIG. 2 (a) as indicated by an arrow c in FIG. While the developer is being stirred by the spiral fin 48, as shown by the arrow e in FIG. 2 (a), the developer is conveyed from the near side in the depth direction of the drawing to the other side (left side indicated by the arrows h, i, and j in FIG. 3). Then, the developer is supplied to the developing roller 15.

  The developing roller 15 supplies only the developer toner to the photosensitive drum 10 shown in FIGS. 1, 2A, and 2B, and converts the electrostatic latent image on the circumferential surface of the photosensitive drum 10 into a toner image. (develop. The developer carrier on the developing roller 15 from which only the toner is taken up by the photosensitive drum 10 is mixed with the developer in the developing tank 43a.

  The developer is sent back to the developing tank 43b from the first circulation port 57 on the other side (left side in FIG. 3) in the depth direction of FIG. 2A and 2B, as indicated by an arrow k.

  The second agitating / conveying member 17 in the developing tank 43b rotates counterclockwise as indicated by an arrow d in FIG. 2A, and the developer in the developing tank 43b is agitated by the spiral fins 51. Then, as indicated by the arrow f, the sheet is conveyed from the far side in the depth direction of the sheet of FIG.

  The second agitating / conveying member 17 stirs and conveys the developer from the second circulation port 67 on the near side in the depth direction in FIG. 3 (a) and 3 (b) (right side in FIG. 3) by the arrow p. As shown, the developer is sent to the developing tank 43a. In this way, the reflux of the developer and the replenishment of the toner are repeated, and the development with the toner proceeds sequentially.

  Although not shown in FIG. 1, the printer 1 of the present example has an electrical component disposed at the rear left part of the main unit, and a circuit in which a control device composed of a plurality of electronic components is mounted on the electrical component. The base is attached.

  FIG. 4 is a circuit block diagram including the control device of the printer 1 described above. As shown in FIG. 4, the circuit block is centered on a central processing unit (CPU) 70, and an interface controller (I / F_CONT) 71 and a printer controller (PR_CONT) 72 are connected to the CPU 70 via a data bus. ing. A printer printing unit 73 is connected to PR_CONT 72.

  Also connected to the CPU 70 are a ROM (read only memory) 74, an EEPROM (electrically erasable programmable ROM) 75, an operation panel 38 of the main body operation unit, and a sensor unit 76 to which outputs from sensors arranged in the respective units are input. ing.

  The ROM 74 stores a system program, and the CPU 70 performs processing by controlling each unit in accordance with the system program.

  That is, in each unit, the I / F_CONT 71 first converts print data supplied from a host device such as a personal computer into bitmap data and develops it in the frame memory 77. In the frame memory 77, storage areas are set for each of black (K), magenta (M), cyan (C), and yellow (Y), and data of each color is developed in the corresponding area.

  The data developed in the frame memory 77 is output to the PR_CONT 72, and is output from the PR_CONT 72 to the printer printing unit 73.

  The printer printing unit 73 is an engine unit, and under the control of the PR_CONT 72, the rotation driving system (not shown) including the photosensitive drum 10, the primary transfer roller 21 and the like shown in FIG. 1, the charging roller 12, the optical writing An image forming unit having a driven unit such as a head 13 and a driving unit (not shown) that drives the transfer belt unit 3 to move up and down and the transfer belt 8 to rotate are provided.

  Further, the printer printing unit 73 includes a belt driving unit 78 that drives the belt of the belt-type fixing unit 6, a toner supply unit motor driving unit 79 that drives the motor of the developing device 14, the developing roller 15, the primary transfer roller 21, the second transfer roller 21, and the like. A high voltage unit drive unit 80 is provided for driving a high voltage unit that applies a high voltage bias to the next transfer roller 24 and the like.

  Further, the printer printing unit 73 is a drive output to a process load such as a conveyance mechanism composed of rotationally driven parts such as the paper take-out roller 22 to the paper discharge roller pair 31, and a belt-type fixing unit 6 that is heated and rotated. To control.

  The print data of black (K), magenta (M), cyan (C), and yellow (Y) output from the PR_CONT 72 is sent from the printer printing unit 73 to the corresponding optical writing head shown in FIG. 13 is supplied.

  Incidentally, a two-component developer is used to develop the electrostatic latent image formed on the photosensitive drum 10 by the optical writing head 13 with the developing device 14. In the two-component development, the carrier and the toner impart a desired charge to the toner by friction caused by mixing and stirring in the developing device.

  The applied charge needs to be an appropriate charge amount. The proper charge amount is the amount of charge necessary for developing the toner. The toner has a charge opposite in polarity to the carrier due to friction with the carrier, and adheres to the carrier due to the charge. The force is proportional to the square of the toner charge amount if the toner particle diameter is the same.

  On the other hand, in order for the toner to contribute to development, it is necessary to overcome the adhesion force with the carrier. The force for pulling the toner away from the carrier is proportional to the electrostatic latent image on the photosensitive drum, the strength of the electric field due to the developing bias applied from the developing roller to the carrier, and the charge of the toner.

  That is, if the charge of the toner is large, the force that the toner is peeled off from the carrier and developed becomes large. The adhesion force to the carrier is proportional to the square of the charge amount of the toner, and the force with which the toner is detached from the carrier is proportional to the charge amount of the toner.

  From this, it is well known that whether or not the toner is developed is defined by a quadratic equation of the charge amount of the toner, and there is a value of the charge amount of the toner that is most easily developed when a solution is obtained. This is considered to be the most appropriate charge amount.

  FIG. 5 is a graph showing the result of measuring the toner charge amount distribution in the same two-component developer as usual. In this measurement, 92 parts of a ferrite carrier having an average particle diameter of 40 μm coated with a silicon resin coat and 8 parts of toner having an average particle diameter of 7 μm were mixed and stirred in advance to prepare a developer as a two-component developer.

  A part of this developer is mounted on a flying charge measuring device as a sample, and the flying toner amount and charge amount at that time are measured while varying the electric field strength applied to the developer. Asked.

  In addition, the flying charge amount measuring device is a device in which an electric field is generated between a metal cylinder having a magnet disposed inside and a metal cylinder disposed on the outer periphery thereof, and the developer placed on the inner cylinder is placed outside. This is a measuring apparatus that can measure the amount of charge of the toner adhering to the outside by flying to the cylinder. The internal magnet rotates to loosen the developer.

  FIG. 5 shows the result of measurement with such a measuring apparatus as a solid line. Here, the average charge amount is about 30 μC / g, but the measurement results show that the charge amount distribution has a wide range from 20 μC / g to 45 μC / g.

  The broken line shown in FIG. 5 indicates that the developer is mounted on the developing device, printed 1000 sheets, a part of the developer in the developing device is sampled, and the charge amount distribution is measured by the flying charge amount measuring device. It shows the result of measuring.

  It can be seen that the curve has a dent in the vicinity of 30 μC / g, and the distribution has spread throughout. This indicates that the toner is selectively developed (used) to some extent. The charge amount portion in the vicinity of 30 μC / g is considered to be an appropriate charge amount range in the developing device.

  Until now, the charge amount and charge amount distribution of toner and carrier have been designed so that the charge amount of the toner to be developed efficiently can be obtained. However, the charge amount and charge amount distribution of the toner may be greatly affected by temperature and humidity.

  The resin coat of the carrier has been effective in reducing the influence of this temperature and humidity, but is still insufficient. In addition, this influence is remarkable in a polymer toner prepared by dispersion in water or a toner using a plant-derived resin containing a large amount of hydroxyl groups, which has been actively developed in recent years.

  Regarding the change in environmental temperature and humidity, the moisture content of toner and carrier decreases under low humidity, the charge amount increases, and the charge amount distribution also widens. On the other hand, moisture adsorption occurs under high humidity and the charge amount decreases. In particular, a polymerized toner having many adsorption sites and a toner using a plant-derived resin are remarkable.

  As a result, the charge amount distribution moves in the high direction or in the low direction, resulting in a decrease in the amount of toner in the proper range required for development.

  For example, the initialization charging potential of the photosensitive drum 10 is “−650 V (volt)”, the potential of the electrostatic latent image attenuated by the exposure of the optical writing head 13 is “−50 V”, and the developing roller 15 is developed. The bias is set to “−250V”.

  In the electric field formed by “−50V” of the electrostatic latent image and “−250V” of the developing roller 15, the charge amount of the toner for transferring an appropriate amount of toner to the electrostatic latent image is around “30 μC / g”. It has been found by the measurement test described above.

  It is also well known that the value of the charge amount varies depending on the size of the toner particles. Since it is impossible to make toner particles have a uniform particle size and a uniform charge amount from the manufacturing method thereof, the distribution curve of the initial charge amount is almost as shown by the solid line in FIG. It becomes a normal distribution and the skirt spreads from side to side.

  The present invention seeks to secure a toner having a charge amount in an appropriate range regardless of environmental fluctuations in a developer using a mixture of carrier and toner.

  More specifically, a developer having a wide range of charging functions is realized by mixing two or more types of carriers having different charging functions. One carrier has a proper charge amount range under low humidity, and the other carrier has a proper charge amount range under high humidity.

  FIGS. 6A, 6B, and 6C are diagrams showing the distribution of charge amount in each environment of the developer composed of the two-type mixed carrier and the toner of the present invention.

  FIG. 6A shows the charge amount distribution at room temperature and normal humidity (25 ° C., 50%), and the first carrier C1 has an average charge amount of 23 μC / g. The second carrier C2 has an average charge amount of 41 μC / g. The developer D was obtained by mixing these two types of carriers and toner.

  The average charge amount of the developer D was about 30 μC / g as shown in FIG. When printing was repeated using the mixed developer D, a good image was obtained. The proper range of the toner charge amount varies depending on the conditions of the apparatus such as the potential of the photosensitive drum and the developing bias, but in this example, the vicinity of 30 μC / g appears to be appropriate.

  FIG. 6B is a diagram in which the charge amount distribution is measured after the developer D is left in a low temperature and low humidity environment of 10 ° C. and 20% and sufficiently dried. The first carrier C1 has a high charge amount by about 10 μC / g on average, and the second carrier C2 has a high value by about 15 μC / g on average.

  As shown in FIG. 6B, the developer D containing these two carriers has a wide charge amount distribution and includes a range of charge amount of 30 μC / g that seems to be appropriate. When printing was repeated using the developer D in this environment, the image density was slightly low, but it was sufficiently practical. By adding a slight correction such as a developing bias, a better image can be obtained.

  FIG. 6 (c) is a diagram in which the charge amount distribution is measured after leaving the developer D in a high temperature and high humidity environment of 30 ° C. and 80% and sufficiently containing water. The average charge amount of the first carrier C1 is reduced to 10 μC / g, and the average charge amount of the second carrier C2 is reduced to 30 μC / g.

  It can be seen that a small amount of toner in the vicinity of the charge amount of 30 μC / g, which is considered to be an appropriate charge amount of the developer D, can be secured. By selectively consuming this portion, it is possible to avoid an extreme deterioration in image quality under a high humidity environment.

  As described above, according to the developer D of the present invention, deterioration of image quality can be prevented by including a toner having an appropriate charge amount in the developer under any environment.

  The charging ability of the carrier can be easily and arbitrarily controlled by mixing the type of resin coated on the carrier and mixing a charge control agent or a conductive agent into the resin. Further, the charging ability of the toner can be determined by the electric characteristics of the resin used for the toner, the electric characteristics of the pigment as the colorant, and the characteristics of the charge control agent.

  As described above, in the two-component developer using a mixture of nonmagnetic toner and magnetic carrier, the first magnetic carrier that imparts an appropriate triboelectric charge amount to the toner in a low humidity environment, and the high humidity environment By mixing and using a second magnetic carrier that imparts an appropriate triboelectric charge amount to the toner, it is possible to obtain an appropriate toner charge distribution for development even when the usage environment fluctuates. Images can be created.

Although several embodiments of the present invention have been described, the present invention is included in the invention described in the claims and the equivalents thereof. Hereinafter, the invention described in the scope of claims of the present application will be appended.
[Appendix 1]

By mixing the toner alone with the toner, the first carrier having the largest amount of toner of the first charge amount per unit weight of the mixture obtained by mixing with the toner alone, and the toner alone A two-component developer is formed by mixing a second carrier having the largest amount of toner having a second charge amount different from the first charge amount per unit weight of the resulting mixture. A two-component developer forming method.
[Appendix 2]

The first carrier is a carrier having a lower charging property than the second carrier,
In the mixture obtained by mixing the first carrier, the second carrier and the toner, the third charge amount per unit weight at which the toner amount is the largest is greater than the first charge amount. Large and smaller than the second charge amount,
The method for forming a two-component developer according to supplementary note 1, wherein:
[Appendix 3]

In a room temperature and humidity environment, the third charge amount corresponds to an appropriate charge amount.
The method for forming a two-component developer according to Supplementary Note 2, wherein:
[Appendix 4]

In a low temperature and low humidity environment,
Both the first charge amount, the second charge amount, and the third charge amount are larger than those in a normal temperature and humidity environment,
The first charge amount corresponds to an appropriate charge amount;
The method for forming a two-component developer according to Supplementary Note 2 or 3, wherein:
[Appendix 5]

In a high temperature and high humidity environment,
The first charge amount, the second charge amount, and the third charge amount are all smaller than those in a normal temperature and humidity environment,
The second charge amount corresponds to an appropriate charge amount;
The two-component developer forming method according to any one of appendices 2 to 4, characterized in that:
[Appendix 6]

An image forming apparatus using a two-component developer according to the two-component developer forming method according to any one of appendices 1 to 5.
[Appendix 7]

  A developer formed by the two-component developer forming method according to any one of appendices 1 to 5.

  INDUSTRIAL APPLICABILITY The present invention can be used for a two-component developer forming method, an image forming apparatus, and a developer that optimize the charge distribution of a toner that is suitable for development that always produces a good image even when the usage environment varies.

1 Full-color image forming device (printer)
DESCRIPTION OF SYMBOLS 2 Image formation part 3 Transfer belt unit 4 Toner supply part 5 Paper feeding part 6 Belt type fixing unit 8 Transfer belt 8a Lower running part surface 9 (9m, 9c, 9y, 9k) Developing device 10 Photosensitive drum 11 Cleaning blade 12 Roller 13 Optical writing head 14 Developer 15 Developing roller 16 First stirring and conveying member 17 Second stirring and conveying member 18 Drive roller 19 Followed roller 21 Primary transfer roller 23 Secondary transfer unit 24 Belt cleaner 25 Cleaning blade 26 Waste toner Collection container 27 (27m, 27c, 27y, 27k) Toner hopper 29 Paper feed cassette 30 Paper 31 Paper take-out roller 32 Feeding roller 33 Rolling roller 34 Standby conveyance roller pair 35 Secondary transfer roller 36 Diffuse reflection type density sensor 37 Paper discharge Tray 38 Operation panel 41 Wall frame 41a, 41b Developing roller support 41c Extending outer wall frame 42 Internal partition wall 43 Developing tank 43a First developing tank 43b Second developing tank 44 Doctor blade 45 Toner density sensor 45y Y toner density sensor 45m M toner density sensor 45c C toner density sensor 45k K toner density sensor 46 Detection surface 47 Rotating shaft 47a Outer end 48 Spiral fin 49 Rotating shaft 51 Spiral fin 52 Blade holder 53 Elastic sheet (blade)
54 Cleaning blade 55 Rotating shaft 56 Gear 57 First circulation port 58 Toner supply port 59 Drive relay gear 61 External engagement gear 62 Drive transmission gear 63 Motor 64 Rotating shaft 65 Drive gear 66 (66y, 66m, 66c, 66k) Development Rotator 67 Second circulation port 70 CPU (central processing unit)
71 Interface controller (I / F_CONT)
72 Printer controller (PR_CONT)
73 Printer printing section 74 ROM (read only memory)
75 EEPROM (electrically erasable programmable ROM)
76 Sensor unit 77 Frame memory 78 Belt drive unit 79 Toner supply unit Motor drive unit 80 High voltage unit drive unit

Claims (7)

  By mixing the toner alone with the toner, the first carrier having the largest amount of toner of the first charge amount per unit weight of the mixture obtained by mixing with the toner alone, and the toner alone A two-component developer is formed by mixing a second carrier having the largest amount of toner having a second charge amount different from the first charge amount per unit weight of the resulting mixture. A two-component developer forming method. The first carrier is a carrier having a lower charging property than the second carrier,
In the mixture obtained by mixing the first carrier, the second carrier and the toner, the third charge amount per unit weight at which the toner amount is the largest is greater than the first charge amount. Large and smaller than the second charge amount,
The two-component developer forming method according to claim 1. In a room temperature and humidity environment, the third charge amount corresponds to an appropriate charge amount.
The two-component developer forming method according to claim 2. In a low temperature and low humidity environment,
Both the first charge amount, the second charge amount, and the third charge amount are larger than those in a normal temperature and humidity environment,
The first charge amount corresponds to an appropriate charge amount;
The two-component developer forming method according to claim 2, wherein the two-component developer is formed. In a high temperature and high humidity environment,
The first charge amount, the second charge amount, and the third charge amount are all smaller than those in a normal temperature and humidity environment,
The second charge amount corresponds to an appropriate charge amount;
The two-component developer forming method according to claim 2, wherein the two-component developer is formed.   An image forming apparatus using the two-component developer according to the two-component developer forming method according to claim 1. A developer formed by the two-component developer forming method according to any one of claims 1 to 5.