JP4919748B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device and an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic printer, it is well known that an image is formed by each process of charging, exposure, development, transfer, fixing, and cleaning. In the development process among these processes, a developing roller as a toner carrier is brought into contact with a photosensitive drum as an electrostatic latent image carrier, and a voltage is applied to the developing roller. A contact-type developing device using a non-magnetic one-component toner that develops an electrostatic latent image is often used because of the advantages of downsizing and cost reduction.

  In such a developing device, a toner regulating blade for forming a thin layer of toner as a developer on the developing roller in pressure contact with the developing roller, and a foam for supplying toner to the developing roller A supply roller made of steel is installed. The toner is first supplied to the supply roller, and then supplied from the developing roller to the photosensitive drum. In this case, the toner is loaded on foam bubbles formed on the outer peripheral surface of the supply roller, and is sent to the developing roller according to the rotation of the supply roller. At this time, the surface of the supply roller and the surface of the developing roller are rubbed with each other through the toner, whereby the toner is frictionally charged, and the charged toner is attracted to and attached to the developing roller.

In such a developing device, in order to make the toner conveying ability uniform to the developing roller, a technique for making the cell diameter of the foam of the supply roller larger than 1/2 of the average particle diameter of the toner and less than 10 times is proposed. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 10-48940

  However, in the conventional developing device, when toner having high fluidity is used, density unevenness and fogging of non-image portions may occur. In recent years, for example, there is a strong demand for higher resolution of 1200 [dpi] or more, and in order to meet such a demand, improvement in toner fluidity is required. Since the toner having high fluidity has less aggregation between particles, it is advantageous for reproducing fine lines and isolated dots in the development process. The toner having high fluidity has a small physical adsorption force to the surface of the photosensitive drum, and white spots and the like hardly occur in the transfer process. However, when a highly fluid toner is used, density unevenness is likely to occur and fogging is likely to occur in the non-image area.

  The present invention solves the problems of the conventional developing device, and determines the average foam cell diameter of the foam of the supply member according to the degree of condensation of the toner, whereby the toner adhering to the non-image portion of the image carrier An object of the present invention is to provide a developing device and an image forming apparatus that can reduce the amount of toner and that does not cause density unevenness or fog.

For this purpose, in the developing device of the present invention, the toner is carried by supplying toner to the image carrier carrying the electrostatic latent image, and the toner is brought into contact with the toner carrier and rotated to rotate the toner. A developing device having a supply member provided with a foam to be supplied to the toner carrier, wherein the toner aggregation degree is a [%], and the average foam cell diameter of the supply member foam is b [μm]. When satisfying the relationship of 10 ≦ a ≦ 50 and 2 × a ≦ b ≦ 3 × a, the toner carrier and the supply member are in pressure contact, and the biting distance between the toner carrier and the supply member is c [ mm], and the thickness of the foam of the supply member is d [mm], the relationship of 1.0 ≦ c ≦ 0.5 × d (where 2.0 ≦ d) is satisfied, and the toner of the supply member stress on bearing member, 1.2 [N / cm] or more, 2 5 is [N / cm] or less.

  According to the present invention, the developing device determines the average foam cell diameter of the foam of the supply member according to the degree of toner condensation. As a result, the amount of toner adhering to the non-image portion of the image carrier can be reduced, and density unevenness and fogging can be prevented.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 is a schematic configuration diagram of the image forming apparatus according to the first embodiment of the present invention.

  In the figure, reference numeral 10 denotes an image forming apparatus having an image forming unit 20 and a fixing device 30 as image forming units. Here, the image forming apparatus 10 is, for example, a printer, a facsimile machine, a copying machine or the like, and is printed in monochrome or color on a recording medium such as a printing paper, an envelope, or an OHP (Over Head Projector) sheet by an electrophotographic method. An image is formed. The fixing device 30 fixes the toner image on the recording paper 26. The image forming apparatus 10 may form a monochrome image or a color image. In the present embodiment, the image forming apparatus 10 is a color printer that forms a color image. Will be described.

  In this case, the four image forming units 20 corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) move along the conveyance path of the recording paper 26 in the conveyance direction (left in the drawing). Are arranged in order. Since each of the four image forming units 20 has basically the same structure, only one of them will be described here.

  The image forming unit 20 is formed in a drum shape and has a photosensitive drum 11 as an image carrier using an organic photosensitive member on the surface, a charging roller 12 disposed around the photosensitive drum 11, exposure, and the like. It has a device 13, a developing device 14 and a transfer device 15. The charging roller 12, the developing device 14, and the transfer device 15 are disposed so as to contact or press contact with the surface of the photosensitive drum 11. A cleaning blade 16 is provided in contact with the surface of the photosensitive drum 11 in order to scrape and process the toner remaining on the surface of the photosensitive drum 11.

  The exposure device 13 includes an LED (Light Emitting Diode) head, for example, and irradiates the surface of the photosensitive drum 11 with light corresponding to an image signal, thereby forming an electrostatic latent image on the surface.

  In addition, the developing device 14 charges a developing roller 21 as a toner carrying member that contacts the photosensitive drum 11 during printing, and a toner as a supply member that charges the toner replenished from the toner cartridge 22 and supplies the toner to the developing roller 21. It has a supply roller 24 and a layer regulating blade 25 as a layer regulating member that contacts the surface of the developing roller 21 and thins the toner supplied from the toner supply roller 24. In the drawing, reference numeral 23 denotes toner filled in the toner cartridge 22.

  Further, the transfer device 15 is in contact with the photosensitive drum 11, a transfer belt 31 that transfers a toner image to the recording paper 26, a transfer roller 32 that applies a voltage to the transfer belt 31, and the most downstream of the transfer belt 31. And a cleaning blade 34 for cleaning the transfer belt 31.

  A fixing device 30 is disposed on the downstream side of the four image forming units 20 in the conveyance path of the recording paper 26.

  The operations of the photosensitive drum 11, the charging roller 12, the exposure device 13, the developing roller 21, the toner supply roller 24, the transfer roller 32, the driving rollers 33a and 33b, and the fixing device 30 are controlled by a control unit (not shown). . The control unit applies a high DC voltage from a power source (not shown) to the charging roller 12, the transfer roller 32, the developing roller 21, and the toner supply roller 24 at a predetermined timing. The photosensitive drum 11, the charging roller 12, the driving rollers 33a and 33b, the developing roller 21, and the toner supply roller 24 are rotationally driven by a driving motor (not shown).

  Next, the toner in this exemplary embodiment will be described.

  As a result of repeated research, the inventors of the present invention have found that the toner fluidity and the foam cell diameter of the toner supply roller have an effect on fog. Hereinafter, the result of detailed investigation on the relationship between the toner fluidity and the foam cell diameter of the toner supply roller will be described.

  The toner in this exemplary embodiment includes polyester as a binder resin, carbon black as a colorant, copper phthalocyanine pigment (CI Pigment Blue 15), quinacridone pigment (CI Pigment Red 122), C.I. I. This is a pulverized toner using Pigment Yellow 185 or the like. The toner has an average particle diameter of 5.8 [μm], and an additive is externally added for the purpose of controlling the fluidizing agent and chargeability.

  Examples of the additive include titanium oxide, alumina, silica, and the like, and the silica is subjected to silicone oil treatment or disilazane treatment. Examples of the primary particle diameter of the additive include 7 [nm], 12 [nm], 14 [nm], 21 [nm], and 40 [nm]. These additives are combined, mixed with toner using a Turbula mixer or Henschel mixer, and externally added. Depending on the combination and mixing conditions of these additives, a toner having a desired fluidity can be obtained. For example, increasing the amount of additive having a small particle size can increase the fluidity of the toner.

In the present exemplary embodiment, the degree of aggregation serving as an index of toner fluidity was measured by the following methods (1) to (4) using MULTI TESTER MT-1001 (manufactured by Seishin Enterprise Co., Ltd.). The measurement environment was 23 [° C.] and 50 [%], and the toner to be measured was left in this environment for 24 hours or more.
(1) Weigh out 2.0 [g] of toner with a precision balance.
(2) From the top, a 100 mesh (opening 150 [μm]), 200 mesh (opening 75 [μm]), 400 mesh (opening 38 [μm]) sieve is placed on the measuring device. set.
(3) Gently place 2.0 [g] of toner on a 100-mesh sieve and vibrate for 90 seconds with an amplitude of 1.0 [mm].
(4) Gently measure the amount of toner remaining on each sieve with a precision balance.

The toner aggregation degree a can be obtained by the following equation (1).
a = x + y + z [%] (1)
here,
x = (amount of toner remaining on 100 mesh) [g] /2.0×100
y = 0.6 × (amount of toner remaining on 200 mesh) [g] /2.0×100
z = 0.2 × (amount of toner remaining on 400 mesh) [g] /2.0×100
It is.

  The smaller the toner cohesion degree a, the higher the toner fluidity, and the smaller the cohesion force between the toners and the adhesion force to the wall surface.

  In this embodiment, a toner having an aggregation degree of 10% to 50% is used. When the toner cohesion is less than 10%, the toner has very high fluidity and becomes a smooth toner. Therefore, it is difficult to seal the toner so that the toner does not leak from the developing device 14. Further, when the toner aggregation degree is larger than 50%, it is difficult to reproduce fine lines and isolated dots, which is not the purpose of improving the image quality with the high fluidity toner, which is the original problem.

  Next, the developing device 14 in the present embodiment will be described in detail.

  FIG. 3 is a diagram showing a developing roller and a toner supply roller of the developing device according to the first embodiment of the present invention.

  The layer regulating blade 25 is a member in which a 0.08 mm thick SUS304 metal plate having a spring property is molded into an L shape as shown in the figure, and its edge portion is formed on the surface of the developing roller 21. It is installed so as to be pressed.

  The developing roller 21 has a metal shaft 35 and an elastic body 36 attached to the outer periphery of the shaft 35. In the present embodiment, a semiconductive urethane rubber having a thickness of 4 mm and a rubber hardness of 70 degrees (Asker C) is attached as an elastic body 36 to the outer periphery of a metal shaft 35 having a diameter of 12 mm. The surface layer of the elastic body 36 is subjected to predetermined treatment for the purpose of adjusting the friction coefficient, roughness, charging characteristics and the like.

  Further, the toner supply roller 24 includes a metal shaft 37 and a foam 38 attached to the outer periphery of the shaft 37. In the present embodiment, a urethane foam having a thickness of 5 mm and a hardness of 50 degrees (Asker F) is attached to the outer periphery of a metal shaft 37 having a diameter of 6 mm as the foam 38. The toner supply roller 24 is disposed so as to be in pressure contact with the developing roller 10, and the pressure is 0.6 [N / cm].

  In this embodiment, the toner supply roller 24 having the foam 38 having an average foam cell diameter of 20 to 200 [μm] was prepared and evaluated. The foam cell diameter of the foam 38 can obtain a desired value by changing the amount and type of the foaming agent, controlling the vulcanization time, and the temperature. For example, to increase the foam cell diameter, there are methods such as increasing the amount of foaming agent, increasing the vulcanization time, and increasing the vulcanization temperature.

  Next, a method for measuring the average foamed cell diameter in the present embodiment will be described.

  FIG. 4 is a diagram showing a method of measuring the average foamed cell diameter of the toner supply roller in the first embodiment of the present invention.

  First, an image of the surface of the toner supply roller 24 is taken using a digital microscope VHX-200 (manufactured by Keyence Corporation), and 50 holes are taken out at random and the area of each hole is measured. 4A shows a minute portion on the surface of the toner supply roller 24, and FIG. 4B shows an enlarged state of the minute portion 41. In FIG.4 (b), the part to which the number of 1, 2, 3, ... was attached | subjected is a hole. The attached image processing software was used to measure the area of each hole. At this time, only the holes where all the images are shown in the image were measured.

  From the area of the 50 holes thus measured, the equivalent circle diameter (the diameter of the circle corresponding to the area) was determined, and the average value was taken as the average foamed cell diameter. In FIG. 4C, reference numeral 42 denotes a hole to be measured, and S1 denotes an area of the hole 42. 43 is a circle having the same area S1 as the hole 42, and 44 is the diameter of the circle 43, that is, the equivalent circle diameter of the hole 42.

  Next, the operation of the image forming apparatus 10 having the above configuration will be described.

  When a printing command is input from a host device (not shown), such as a personal computer, the control unit of the image forming apparatus 10 causes the photosensitive drum 11 to rotate around the photosensitive drum 11 in a direction indicated by an arrow in FIG. Rotate at speed. Then, a DC voltage is applied to the charging roller 12 disposed so as to be in contact with or pressure contact with the surface of the photosensitive drum 11 to uniformly and uniformly charge the surface of the photosensitive drum 11. In the present embodiment, a DC voltage of −1150 [V] is applied to the charging roller 12. At this time, the charged potential of the surface of the photosensitive drum 11 was about −650 [V].

  Next, in the exposure process, the exposure device 13 irradiates the surface of the photosensitive drum 11 with light corresponding to the image signal, and an electrostatic latent image is formed on the surface.

  The toner replenished from the toner cartridge 22 is supplied to the developing roller 21 by the rotation of the toner supply roller 24 to which a voltage is applied by a high voltage power supply for a toner supply roller (not shown). In the present embodiment, a DC voltage of −330 [V] is applied to the toner supply roller 24. The developing roller 21 and the toner supply roller 24 rotate in the same direction, and the peripheral speed of the toner supply roller 24 is 0.6 times the peripheral speed of the developing roller 21. The developing roller 21 attracts the toner and conveys it in the direction indicated by the arrow. Then, a thin layer of the toner layer is formed on the surface of the developing roller 21 by the layer regulating blade 25 that is pressed against the developing roller 21 on the downstream side in the rotation direction and applied with a DC voltage of −330 [V] by a high voltage power source (not shown). It is formed. In the present embodiment, the contact pressure between the layer regulating blade 25 and the developing roller 21 is set to about 0.8 [N / cm].

  The toner that has passed through the layer regulating blade 25 is further conveyed by the rotational movement of the developing roller 21 in the direction indicated by the arrow, and develops the electrostatic latent image formed on the photosensitive drum 11. In this embodiment, it is assumed that reversal development is performed, and a bias voltage is applied between a conductive support (not shown) of the photosensitive drum 11 and the developing roller 21 by a high voltage power supply (not shown). In this case, a DC voltage of −200 [V] is applied to the developing roller 21. An electric line of force accompanying the electrostatic latent image formed on the photosensitive drum 11 is generated between the developing roller 21 and the photosensitive drum 11. For this reason, the charged toner on the developing roller 21 adheres to the photosensitive drum 11 by electrostatic force, and the electrostatic latent image is developed with the toner to form a toner image.

  On the other hand, the transfer belt 31 rotates in the direction indicated by the arrow by the rotation of the drive rollers 33a and 33b, and the recording paper 26 supplied from a paper feed cassette (not shown) is sent to the transfer section by the transfer belt 31. A voltage is applied to a transfer roller 32 provided opposite to the photosensitive drum 11 by a high voltage power source (not shown), and the toner image formed on the photosensitive drum 11 is transferred to the recording paper 26.

  Thereafter, the recording paper 26 is further conveyed to the fixing device 30 by the transfer belt 31, and the toner is melted by receiving heat and pressure. The melted toner penetrates between the fibers of the recording paper 26 and is fixed to the recording paper 26. Is done. The recording paper 26 on which the toner image is fixed is sent out of the image forming apparatus 10.

  On the other hand, some toner may remain on the surface of the photosensitive drum 11 after the transfer, but this residual toner is removed by the cleaning blade 16. Thus, the photosensitive drum 11 is repeatedly used.

  Next, the relationship between the degree of toner aggregation and the average foam cell diameter of the foam 38 of the toner supply roller 24 in the present embodiment will be described.

  FIG. 1 is a graph showing experimental results on the relationship between the degree of aggregation of toner and the average foam cell diameter of the foam of the toner supply roller in the first embodiment of the present invention.

  In the present embodiment, toner having a cohesion degree of 10 to 50 [%] and a toner supply roller 24 having an average foamed cell diameter of the foam 38 of 20 to 200 [μm] are used, and fogging is performed at 0 [%] density printing. The range in which a good printing result with a Macbeth density of 1.2 or more was obtained by printing was confirmed by experiments.

In the evaluation of fog, the image forming apparatus 10 is stopped in the middle of printing at 0% density, and the toner on the photosensitive drum 11 after development and before transfer is adhesive tape (Scotch Mending Tape manufactured by Sumitomo 3M). Adhered to. Then, the adhesive tape to which the toner is adhered is pasted on the recording paper 26, and the color difference ΔE from the one in which only the adhesive tape is pasted on the recording paper 26 is measured by a spectrocolorimeter (CM2600d manufactured by Konica Minolta). did. A small value of the color difference ΔE indicates that there is little fogging. Note that the evaluation standard of the color difference ΔE is set as follows by the US Standards Bureau.
ΔE 0-0.5 trace (feels faint)
ΔE 0.5 to 1.5 slight (slightly felt)
ΔE 1.5-3.0 noticable (can be felt quite)
ΔE 3.0-6.0 appreceable (conspicuously felt)
ΔE 6.0-12 much (feels great)
ΔE 12 to very much (feels very large)
That is, if the value of ΔE is 0.5 or less, the color is the same, and if it is in the range of 0.5 to 1.5, there is a slight difference, but it is not considered to be considered as a different color. The inventor of the present invention collected the toner on the photosensitive drum 11 with an adhesive tape and evaluated the color difference. However, not all the toner on the photosensitive drum 11 is transferred to the recording paper 26. The toner transfer rate also changes depending on the type of the recording paper 26. However, even with the above evaluation method, if the value of ΔE is 1.0 or less, the value of ΔE is always 1.0 or less even on the recording paper 26 medium after printing, and there is no problem in print quality. Judge the level.

  When the print density is 1.2 or more, the image quality when gradation (area gradation) printing is performed can be improved. That is, if gradation printing is performed at a printing density of less than 1.2 at the time of solid printing, the reproducibility of each pixel is remarkably deteriorated, and it becomes impossible to express an appropriate gradation density, resulting in blurring. Will occur. Therefore, when the printing density is 1.2 or more, the image quality can be improved even if gradation printing is performed, and the accuracy of 150 gradations, which is the human eye identification range, can be expressed.

  The results of an experiment regarding the relationship between the degree of toner aggregation and the average foam cell diameter of the foam 38 of the toner supply roller 24 in the present embodiment are as shown in FIG.

  From the figure, when the toner aggregation degree a is small, the density can be secured even if the average foam cell diameter b of the foam 38 of the toner supply roller 24 is small, but when the toner aggregation degree a is large. It can be seen that the concentration cannot be secured unless the average foamed cell diameter b is increased. This is because a toner having a high cohesion degree a has a strong adhesion force to the cell wall surface and a cohesion force between toner particles, so even if toner is present in the cell, it is close to the surface layer and is in direct contact with the cell wall surface. This is because only a part of the toner that is not present is supplied to the developing roller 21. For this reason, when the cell diameter is small and the contact area between the cell wall surface and the toner is large, the toner supply amount becomes insufficient, and the density is lowered or drowned.

From the results of the experiment shown in the figure, the relationship between the toner aggregation degree a [%] and the average foam cell diameter b [μm] of the foam 38 of the toner supply roller 24 is set as shown in the following formula (2). By doing so, it can be seen that the density during 100 [%] density printing can be secured to 1.2 or more.
2 × a ≦ b Formula (2)
However, the average foam cell diameter b of the foam 38 of the toner supply roller 24 is not necessarily large. As the average foam cell diameter b increases, the cell depth increases accordingly. For this reason, the amount of toner loaded in the cell increases, and the toner cannot be sufficiently charged in a region where the developing roller 21 and the toner supply roller 24 come into contact with each other to apply frictional charging to the toner. Then, a toner that is insufficiently charged or a toner charged to a reverse polarity due to friction between the toners appears as fog.

Therefore, the relationship between the toner aggregation degree a [%] and the average foam cell diameter b [μm] of the foam 38 of the toner supply roller 24 is set as shown in the following formula (3), whereby the photosensitive drum 11 can reduce the amount of fog toner adhering to the non-image area on the image 11 and improve the fog on the printed image.
b ≦ 3 × a Formula (3)
In the present embodiment, the case where the printing resolution is set to 1200 [dpi] has been described. However, even when the printing resolution is set to a value exceeding 1200 [dpi], for example, 1400 [dpi], the same is true. I was able to get the results.

  As described above, in the present embodiment, the relationship between the toner aggregation degree a [%] and the average foam cell diameter b [μm] of the foam 38 of the toner supply roller 24 is expressed by the above equation (2). By setting, it is possible to ensure a density of 1.2 or more at the time of 100 [%] density printing even in high resolution printing of 1200 [dpi] or more.

  Further, by setting the relationship between the agglomeration degree a [%] of the toner and the average foamed cell diameter b [μm] as in the above equation (3), the fog adhering to the non-image portion on the photosensitive drum 11 is set. The toner can be reduced, and the fog on the printed image can be improved.

  Next, a second embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st Embodiment, the description is abbreviate | omitted by providing the same code | symbol. The description of the same operations and effects as those of the first embodiment is also omitted.

  Even if the relationship between the toner aggregation degree a [%] and the average foam cell diameter b [μm] of the foam 38 of the toner supply roller 24 is set as described in the first embodiment, continuous printing is performed. If the number of printed sheets increases when performing the above, fogging may occur. As a result of repeated research, the inventors of the present invention have found that the biting distance has an influence when the developing roller 21 and the toner supply roller 24 are arranged so as to be in pressure contact with each other. Therefore, in the present embodiment, a result obtained by examining in detail the effects of the developing roller 21, the toner supply roller 24, and the biting distance will be described.

  In the present embodiment, toner having an aggregation degree of 30% is used. Note that the configuration of the image forming apparatus 10 in the present embodiment is the same as that in the first embodiment, and a description thereof will be omitted.

  Next, the developing device 14 in the present embodiment will be described.

  FIG. 5 is a view showing a developing roller and a toner supply roller of the developing device according to the second embodiment of the present invention.

  In this embodiment, the toner supply roller 24 having the foam 38 having an average foam cell diameter of 70 [μm] was prepared and evaluated. The foam cell diameter of the foam 38 can obtain a desired value by changing the amount and type of the foaming agent, controlling the vulcanization time, and the temperature. For example, to increase the foam cell diameter, there are methods such as increasing the amount of foaming agent, increasing the vulcanization time, and increasing the vulcanization temperature.

In the figure, c is the biting distance between the developing roller 21 and the toner supply roller 24. In the present embodiment, the value of the biting distance c is 0.2 [mm], 0.5 [mm], 1.0 [mm], 1.5 [mm], 2.0 [mm], It was 2.5 [mm] and 3.0 [mm]. The biting distance c is expressed by the following equation (4), where r _{1 is} the radius of the developing roller 21, r _{2 is} the radius of the toner supply roller 24, and e is the distance between the axes of the developing roller 21 and the toner supply roller. Can be sought.
c = (r ₁ + r ₂ ) −e Formula (4)
Note that the configuration of other points of the developing device 14 and the method of measuring the average cell diameter in the present embodiment are the same as those in the first embodiment, and a description thereof will be omitted.

  Next, the relationship between fog and biting distance c in the present embodiment will be described.

  FIG. 6 is a diagram showing experimental results on the relationship between fog and biting distance in the second embodiment of the present invention, and FIG. 7 is foam thickness and biting distance in the second embodiment of the present invention. FIG. 8 is a first diagram showing experimental results on the relationship between stress and stress, and FIG. 8 is a second diagram showing experimental results on the relationship between foam thickness, biting distance and stress in the second embodiment of the present invention. FIG.

  In the present embodiment, a toner having a cohesion degree of 30 [%] and a toner supply roller 24 having an average foam cell diameter of 70 [μm] of the foam 38 are used. The value of the biting distance c is 0.2 [mm], 0.5 [mm], 1.0 [mm], 1.5 [mm], 2.0 [mm], 2.5 [mm] and 3 The fog was evaluated by the developing device 14 after printing 30 k sheets of recording paper 26 in the A4 vertical direction. Note that the fog evaluation method is the same as that in the first embodiment, and a description thereof will be omitted.

  The result of the experiment about the relationship between the value of the color difference ΔE indicating fogging and the biting distance c in the present embodiment is as shown in FIG.

  From FIG. 6, it can be seen that when the value of the biting distance c is small, the fog becomes large during continuous printing and the print quality is deteriorated. In the present embodiment, the developing roller 21 and the toner supply roller 24 are disposed in pressure contact with each other and rotate while there is a difference in the peripheral speed between them. Therefore, when the number of printed sheets increases, the toner supply roller 24 is worn due to wear. The diameter becomes smaller. Therefore, in the state after printing 30k sheets, the biting distance c between the developing roller 21 and the toner supply roller 24 is smaller than in the initial state, and the contact area between the developing roller 21 and the toner supply roller 24 is reduced. This is because sufficient frictional charging is not performed. Therefore, it is necessary to set the value of the biting distance c so that a contact area where the toner 23 can be sufficiently triboelectrically charged even if worn is secured.

Therefore, by setting the value of the biting distance c [mm] between the developing roller 21 and the toner supply roller 24 as shown in the following formula (5), it is possible to prevent fogging even after 30k sheets are continuously printed. A printed image can be obtained.
1.0 [mm] ≦ c (5)
However, if the biting distance c is too large, the torque for driving the developing device 14 increases due to the frictional force between the developing roller 21 and the toner supply roller 24. When the biting distance c is smaller than the thickness of the foam 38 of the toner supply roller 24 as shown in FIG. 5, that is, the foam layer thickness d, the developing roller 21 and the toner supply roller 24 The force acting during the period increases almost in proportion to the biting distance c. However, if the bite distance c exceeds half of the foam layer thickness d, the foam cell is sufficiently compressed, so that a very large stress is applied to increase the bite distance c. become.

  FIG. 7 shows the result of measuring the stress value by changing the foam layer thickness d of the toner supply roller 24 in the present embodiment. Moreover, the change of the stress with respect to the ratio of the foam layer thickness d and the biting distance c is as shown in FIG.

From the results of the experiments shown in FIGS. 7 and 8, it can be seen that when the biting distance c exceeds half of the foam layer thickness e, the stress rapidly increases. Therefore, the relationship between the biting distance c [mm] between the developing roller 21 and the toner supply roller 24 and the foam layer thickness d [mm] of the toner supply roller 24 is set as shown in the following equation (6). By doing so, an extreme increase in torque for driving the developing device 14 can be prevented.
c ≦ 0.5 × d (6)
As described above, in the present embodiment, by setting the biting distance c [mm] between the developing roller 21 and the toner supply roller 24 as shown in the above equation (5), the fogging is prevented even after 30k continuous printing. A good printed image that does not occur can be obtained.

  Further, the relationship between the value of the biting distance c [mm] between the developing roller 21 and the toner supply roller 24 and the foam layer thickness d [mm] of the toner supply roller 24 is set as in the formula (6). As a result, an extreme increase in torque for driving the developing device 14 can be prevented.

  Next, a third embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st and 2nd embodiment, the description is abbreviate | omitted by providing the same code | symbol. The description of the same operations and effects as those of the first and second embodiments is also omitted.

  The relationship between the degree of toner aggregation a [%] and the average foam cell diameter b [μm] of the foam 38 of the toner supply roller 24 is set as described in the first embodiment. Even if the biting distance c [mm] between the toner supply roller 24 and the toner supply roller 24 is set as described in the second embodiment, if the number of printed sheets increases when continuous printing is performed, high density printing is performed. Concentration reduction may occur in

  As a result of repeated research, the inventors of the present invention have found that the degree of toner aggregation may increase with the number of printed sheets. This occurs particularly when a silicone material is used for the developing roller 21 or the toner supply roller 24. By analyzing the toner having a high degree of toner aggregation, oligomers which are low molecular components of silicone rubber ooze out from the developing roller 21 or the toner supply roller 24 and are mixed into the toner in the developing device 14. It turns out that this is the cause.

  Therefore, in the present embodiment, a description will be given of the toner supply roller 24 in which density reduction does not occur even when the degree of toner aggregation changes due to continuous printing. In this embodiment, toner having an initial toner aggregation degree of 20% is used. Further, the configuration of the image forming apparatus 10 in the present embodiment is the same as that in the first and second embodiments, and thus the description thereof is omitted.

  Next, the toner supply roller 24 in the present embodiment will be described.

  FIG. 9 is a diagram showing a foam cell of a toner supply roller according to the third embodiment of the present invention.

  In the present embodiment, the toner supply roller 24 has a foam 38 having an average foam cell diameter of 50 [μm] and an average foam cell diameter on the surface of the foam 38 of 50 [μm]. The average foamed cell diameter on the inner side was 100 [μm]. In FIG. 9A, 45 indicates a minute portion on the surface of the foam 38 of the toner supply roller 24, and FIG. 9B shows a state where the minute portion 45 is enlarged.

  The foam cell diameter of the foam 38 can be controlled by the amount and type of the foaming agent, the vulcanization time and temperature, the molding method, and the like. In order to make the foam cell diameter different between the surface layer and the inside like the foam 38 as shown in the figure, for example, a mold molding method in which the foam 38 is foamed in the mold when foamed is used. use. In that case, the surface state of the foam 38 can be controlled by the surface state of the mold.

  Further, in order to reduce the foam cell diameter on the outer peripheral surface of the foam 38, the outer temperature is lowered during vulcanization in molding, and the inner shaft 35 is heated to raise the temperature. It is possible to increase the diameter of the foam cell and reduce the diameter of the outer foam cell.

  In this embodiment, the value of the biting distance c between the developing roller 21 and the toner supply roller 24 is 1.5 [mm]. The method for measuring the average foamed cell diameter is the same as that in the first embodiment, and a description thereof will be omitted.

  Next, the relationship between the number of printed sheets and the image density in the present embodiment will be described.

  FIG. 10 is a first diagram showing experimental results regarding the relationship between the number of printed sheets, the image density, and the degree of toner aggregation in the third embodiment of the present invention, and FIG. 11 shows the printing in the third embodiment of the present invention. FIG. 12 shows the experimental results on the relationship between the number of sheets, the image density, and the degree of toner aggregation, and FIG. 12 shows the experimental results on the relationship between the average foam cell diameter and the amount of wear in the third embodiment of the present invention. FIG. 13 and FIG. 13 are diagrams showing experimental results on the relationship between the average foamed cell diameter and the number of printed sheets in the third embodiment of the present invention.

  In the present embodiment, continuous evaluation was performed using a toner with a cohesion degree of 20% and a toner supply roller 24 with an average foam cell diameter of the foam 38 of 50 μm. At the initial stage and after printing 10k, 20k, and 30k sheets of A4 longitudinal recording paper 26, the measurement of the image density and the measurement of the toner cohesion in 100 [%] printing were performed, respectively. Went. The result was as shown in FIG.

  From FIG. 10, it can be seen that the degree of toner aggregation a increases during continuous printing, and the image density decreases accordingly. That is, since the toner aggregation degree a increases as the number of printed sheets increases, the toner supply roller 24 having an average foamed cell diameter set in accordance with the initial aggregation degree a lacks the toner conveyance capability, and the image density Is thought to have declined. Further, when the thickness of the foam 38 of the toner supply roller 24 is measured after printing 30k sheets, the initial thickness of 5 mm is 4.5 mm, which is caused by friction with the developing roller 21. It was found that the foam 38 was worn by 0.5 [mm].

  Based on such results, a toner supply roller 24 having an average foam cell diameter of 50 [μm] on the surface of the foam 38 and an average foam cell diameter on the inner side of the surface of 100 [μm] is prepared. A continuous evaluation was attempted. Then, at the initial stage and after printing 10k, 20k, and 30k sheets of A4 longitudinal recording paper 26, the measurement of the image density and the toner aggregation degree in 100 [%] printing were performed, respectively. Measurement was performed. The result was as shown in FIG.

  From FIG. 11, it can be seen that the toner aggregation degree a increases during continuous printing, but the image density does not decrease. Further, when the thickness of the foam 38 of the toner supply roller 24 after printing 30k sheets was measured, the initial value of 5 [mm] was 4.5 [mm]. It was confirmed that the foam 38 was worn by 0.5 [mm]. When the average foam cell diameter of the foam 38 was measured, 0.5 [mm] was scraped from the surface due to abrasion with the developing roller 21, and therefore the inner foam cell was exposed, and the value of the average foam cell diameter was The initial value changed from 50 [μm] to 100 [μm]. From this, it can be seen that even when the degree of aggregation a of the toner is reduced, the foam cell diameter is increased, so that a sufficient image density can be secured even in 100% printing.

  As described above, the foam 38 of the supply roller 10 is scraped as the number of printed sheets increases due to abrasion with the developing roller 21. In this Embodiment, the result of having measured the relationship between the abrasion loss of the foam 38 and an average foam cell diameter came to be shown by FIG.

  From FIG. 12, the value of the average foam cell diameter gradually changes from 50 [μm] to 100 [μm] in the range where the wear amount is about 0.2 [mm], and is 100 [μm] in the subsequent range. ] To be constant. The foam cells of the foam 38 of the supply roller 24 have a distribution in the cell diameter and depth, and the foam cells at the shallow depth are exposed with a small amount of wear, for example, 100 [mm]. Further, the foam cell in the deep part is not exposed until the wear amount reaches that value. Therefore, until the foam cell of the surface layer of the foam 38 is completely scraped, the average foam cell diameter gradually changes, and thereafter becomes a value that matches the average foam cell diameter of the deep foam cell. Stabilize.

  In the present embodiment, the foam 38 of the supply roller 24 was worn by 0.5 mm after printing 30 k sheets of A4 longitudinal recording paper 26. Assuming that the number of printed sheets and the amount of wear are in a proportional relationship, the result of measuring the relationship between the number of printed sheets and the average foamed cell diameter is as shown in FIG. 13 indicates a range in which the foamed cell diameter is favorable due to changes in the number of printed sheets and the degree of toner aggregation.

  From FIG. 13, it can be seen that the foamed cell diameter is in a good range even if the degree of aggregation of the toner changes as the number of printed sheets overlaps. As a result, a decrease in image density does not occur and good print quality can be maintained.

  Based on the above results, for example, in the developing device 14 in which the degree of aggregation of the toner is expected to increase with time due to the influence of the oligomer of the silicone roller, the wear of the foam 38 of the toner supply roller 24 is taken into consideration. By reducing the cell diameter of the surface layer of the foam 38 of the toner supply roller 24 and increasing the average foam cell diameter inside the surface, the image density does not decrease even if the degree of aggregation of the toner changes. Printing quality can be maintained.

  That is, the average foamed cell diameter of the foam 38 of the toner supply roller 24 is set to a size that matches the initial aggregation degree of the toner on the surface of the foam 38, and is a size that takes into account the temporal change of the toner aggregation degree inside the surface. It is good to say.

  As described above, in this embodiment, by using the toner supply roller 24 having a larger average foamed cell diameter on the inner side than the average foamed cell diameter on the surface, the print density can be increased over a long period of time. It is possible to obtain a good printed image without deterioration.

  In the first to third embodiments, examples of applying the present invention to an electrophotographic color printer have been described. However, the present invention uses an electrophotographic system such as a monochrome printer or a copying machine. It can also be used for a developing device and an image forming apparatus.

  The present invention is not limited to the above-described embodiment, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

It is a figure which shows the experimental result about the relationship between the aggregation degree of the toner in the 1st Embodiment of this invention, and the average foaming cell diameter of the foam of a toner supply roller. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows the developing roller and toner supply roller of the developing device in the 1st Embodiment of this invention. It is a figure which shows the measuring method of the average foaming cell diameter of the toner supply roller in the 1st Embodiment of this invention. It is a figure which shows the developing roller and toner supply roller of the developing device in the 2nd Embodiment of this invention. It is a figure which shows the experimental result about the relationship between fog and the bite distance in the 2nd Embodiment of this invention. It is a 1st figure which shows the experimental result about the relationship between the foam thickness in the 2nd Embodiment of this invention, the biting distance, and stress. It is a 2nd figure which shows the experimental result about the relationship with the foam thickness in the 2nd Embodiment of this invention, the biting distance, and stress. It is a figure which shows the foam cell of the toner supply roller in the 3rd Embodiment of this invention. It is a 1st figure which shows the experimental result about the relationship between the number of printed sheets, an image density, and the aggregation degree of a toner in the 3rd Embodiment of this invention. FIG. 14 is a second diagram illustrating an experimental result regarding the relationship among the number of printed sheets, the image density, and the degree of toner aggregation in the third embodiment of the present invention. It is a figure which shows the experimental result about the relationship between the average foaming cell diameter and wear amount in the 3rd Embodiment of this invention. It is a figure which shows the experimental result about the relationship between the average foaming cell diameter and the number of printed sheets in the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Photosensitive drum 14 Developing device 21 Developing roller 23 Toner 24 Toner supply roller 38 Foam

Claims (5)

(A) a toner carrier that performs development by supplying toner to an image carrier that carries an electrostatic latent image;
(B) a developing device having a supply member including a foam for supplying toner to the toner carrier by rotating in contact with the toner carrier;
(C) When the aggregation degree of the toner is a [%] and the average foam cell diameter of the foam of the supply member is b [μm],
10 ≦ a ≦ 50, and
2 × a ≦ b ≦ 3 × a
Satisfy the relationship
(D) the toner carrier and the supply member are in pressure contact;
(E) When the biting distance between the toner carrier and the supply member is c [mm] and the thickness of the foam of the supply member is d [mm],
1.0 ≦ c ≦ 0.5 × d (where 2.0 ≦ d)
Satisfy the relationship
(F) The developing device, wherein a stress on the toner carrier of the supply member is 1.2 [N / cm] or more and 2.5 [N / cm] or less. The developing device according to claim 1, wherein the foam of the supply member has a foam cell diameter on a surface smaller than a foam cell diameter on the inside. The developing device according to claim 1, wherein the toner is a one-component toner. The developing device according to claim 1, wherein the toner carrier is in contact with the image carrier. An image forming apparatus comprising the developing device according to claim 1.

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