JP4992589B2 - Toner supply roller and image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus and a toner supply roller used therefor. More specifically, the present invention relates to a toner supply roller and an image forming apparatus using low-hardness urethane as an elastic member.

  Conventionally, in an electrophotographic image forming apparatus, a foamed elastic roller using a foaming material such as urethane is often used as a toner supply roller for supplying toner to a developing roller. In order to reduce frictional heat in a high-speed process image forming apparatus, it has been found that a low-hardness elastic body is suitable as the foamed elastic body used in the toner supply roller. In order to obtain such a low-hardness roller, for example, in Patent Document 1, a foaming agent is mixed with a polyurethane forming material, heated to a temperature equal to or higher than the boiling point of the foaming agent, and after stirring, immediately poured into a mold. A manufacturing method is disclosed.

In addition, there is an image forming apparatus in which a potential difference with respect to the developing roller is provided to the toner supply roller and the toner is supplied to the developing roller by an electric force in order to increase toner supply performance to the developing roller. The toner supply roller used in such an apparatus needs to have a certain degree of conductivity. Therefore, conventionally, a toner supply roller in which a conductive agent is fixed by impregnating a foamed elastic body with a conductive agent dispersion liquid or the like has been often used. That is, the material is first foamed to obtain a foamed elastic body, and then a conductive agent is fixed to the surface. Alternatively, as disclosed in Patent Document 1, there is also a conductive elastic roller manufactured using a material liquid to which a conductivity imparting agent is added.
JP 2000-320536 A

  However, as described above, in the conventional toner supply roller in which the conductive agent is fixed to the surface of the foamed elastic body, the conductive agent may be peeled off due to stress when used for a long time. There is a problem in that the conductivity of the toner supply roller changes depending on the degree of peeling.

  Further, in a toner supply roller manufactured by blending a conductive agent with a material, chemical foaming of the foaming agent may be hindered by the blended conductive agent. In that case, for example, the cell shape may be non-uniform, and therefore the amount of toner contained in the roller may be non-uniform. Another problem is that the hardness of the toner supply roller is increased.

  The present invention has been made to solve the problems of the conventional toner supply roller. That is, an object of the present invention is to provide a toner supply roller manufactured using chemical foaming, which has stable conductivity and low hardness over a long period of time.

  The toner supply roller of the present invention, which has been made for the purpose of solving this problem, is a toner supply roller that has a metal core and a cylindrical foamed elastic layer and supplies toner to the developing roller in the image forming apparatus. The foamed elastic layer is a conductive layer formed by foaming a material mixed with a conductive material component in advance, and the number of cells measured by observing the surface of the foamed elastic layer is 30 to 80. Per unit length in the axial direction when the elastic foam layer is pressed in the radial direction from the outside to 30% of its thickness by using a disk-like pressure member of φ50 mm within the range of 25/25 mm The reaction force is in the range of 10 to 60 mN / mm.

  According to the toner supply roller of the present invention, the foamed elastic layer has an appropriate number of cells and has a moderately low hardness. In addition, since the conductive material component is previously mixed and foamed in the material, it can have stable conductivity over a long period of time. Therefore, the toner supply roller is manufactured by using chemical foaming, and has stable conductivity and low hardness over a long period of time. Here, the reaction force per unit length in the indentation axial direction is substantially the spring constant when the foamed elastic layer is compressed in the radial direction.

  The present invention further includes an image forming apparatus including a photosensitive member, a developing roller, and a toner supplying roller that supplies toner to the developing roller, and the toner supplying roller includes a metal core and a cylindrical foamed elastic layer. And the toner supply roller is measured by observing the surface of the foamed elastic layer, wherein the foamed elastic layer is formed by previously foaming a material mixed with a conductive material component. When the number of cells is in the range of 30 to 80 cells / 25 mm, and the foamed elastic layer is pushed from the outside to 30% of its thickness in the radial direction using a disk-shaped pressure member of φ50 mm The reaction force per unit length in the push-in axial direction extends to an image forming apparatus in the range of 10 to 60 mN / mm.

  Further, in the present invention, the rotational speed of the image bearing member is 200 mm / sec or more, the toner applied by the toner supply roller has a weight average particle size in the range of 4.5 to 7.0 μm, and glass Particularly effective in an image forming apparatus in which the endothermic peaks due to the transition are in two places in the range of 10 to 30 ° C. and 50 to 65 ° C., and the softening point is in the range of 70 to 110 ° C. It is.

  According to the toner supply roller of the present invention, even a toner supply roller manufactured using chemical foaming has stable conductivity and low hardness over a long period of time.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an image forming apparatus having a toner supply roller for supplying a developer to a developing roller.

  The image forming apparatus 10 according to this embodiment includes a photoconductor 11, a developing device 12, and a hopper 13 as shown in FIG. Further, around the photoconductor 11, a charging device 14 that charges the surface of the photoconductor 11 to a predetermined potential, an exposure device 15 that forms a latent image by irradiating the surface of the photoconductor 11 with laser light, and a photoconductor A cleaner 16 that collects the developer remaining on 11 is also provided. Here, the image forming apparatus 10 in which the hopper 13 is provided separately from the developing device 12 is illustrated, but the present invention can also be applied to a single-use image forming apparatus in which the hopper is integrated.

  As shown in FIG. 1, the developing device 12 includes a developing roller 21, a toner supply roller 1, a stirring roller 23, and a conveying roller 24. Further, a conveying member 31 and a stirring member 32 are provided in the hopper 13. A conveyance path 33 for conveying the developer is provided between the hopper 13 and the developing device 12. When the development process according to this embodiment is executed, a bias voltage for the photoconductor 11 is applied to the developing roller 21 and the toner supply roller 1.

  The developing device 12 contains an appropriate amount of developer, is used for image formation, and is appropriately stirred by the stirring roller 23. A new developer is accommodated in the hopper 13 and stirred by a rotating stirring member 32 as indicated by an arrow in FIG. When the developer in the developing device 12 is used and decreases, the developer is supplied from the hopper 13 to the developing device 12. At that time, the developer is supplied to the developing device 12 by the transport member 31 through the transport path 33. In the developing device 12, the toner is transported in the depth direction (the axial direction of the photoconductor 11) by the transport roller 24.

  As shown in FIG. 2, the toner supply roller 1 of this embodiment has a core metal 2 and an elastic body layer 3. The toner supply roller 1 rotates in contact with the developing roller 21 and supplies toner onto the developing roller 21. The elastic layer 3 is softer than the developing roller 21. Therefore, a nip portion is formed mainly by compressing the elastic layer 3 at a contact portion between the developing roller 21 and the toner supply roller 1. In this embodiment, the cored bar 2 is a cylindrical iron cored bar. The elastic body layer 3 is a cylindrical foamed elastic body having through holes formed in the axial direction. The core metal 2 is bonded to the through hole of the elastic body layer 3. Here, D is the thickness of the elastic layer 3 in the free state of the new charging roller 1.

  At the time of image formation, as indicated by arrows in FIG. 1, the photoconductor 11, the toner supply roller 1, and the developing roller 21 are rotated. The surface of the photoreceptor 11 is uniformly charged by the charging device 14 and is partially exposed by the exposure device 15 to form an electrostatic latent image on the surface. The portion of the photoconductor 11 on which the electrostatic latent image is formed is further rotated and then faces the developing device 12. At this time, an appropriate amount of developer is supplied to the surface of the developing roller 21 by the toner supply roller 1. Note that a bias voltage is applied to the toner supply roller 1 during image formation. Further, the electrostatic latent image on the photoconductor 11 is developed at a position facing the developing roller 21. The toner image formed on the photoconductor 11 is transferred to a sheet and fixed in a subsequent process.

  The toner used in the image forming apparatus 10 of the present embodiment has a weight average particle size in the range of 4.5 to 7.0 μm, and an endothermic peak due to glass transition in the range of 10 to 30 ° C. and 50 to There are a total of two places in the range of 65 ° C., and the softening point in the flow tester is in the range of 70 to 110 ° C. Since such a toner is used, the fixing temperature of this embodiment may be about 160 ° C.

  Here, as one of the evaluation methods of the characteristics of the elastic member, there is a method by measuring the magnitude of the reaction force against the indentation. That is, a disc-shaped pressing member having a diameter of 50 mm is pushed from the outside of the new toner supply roller 1 in a direction (radial direction) perpendicular to the cored bar 2. In the toner supply roller 1 of this embodiment, the reaction force in the direction of the push-in axis when pushed to 30% of the initial thickness D in the thickness direction of the elastic layer 3 is in the range of 10 to 60 mN / mm. It has the characteristic.

  This reaction force can be measured as follows, for example. First, a φ50 mm aluminum disc is attached to the tip of a push-pull gauge (manufactured by IMADA, ZP-20N) and pushed into the elastic body layer 3 in a direction perpendicular to the core metal 2. Then, when the thickness h of the elastic layer 3 at the compression point becomes 70% of the thickness D in the initial state, the reaction force in the indentation axial direction is measured. Thus, the reaction force per unit length in the push-in axis direction can be obtained.

  If this reaction force is too large, the elasticity is too high and a sufficient nip width with the developing roller 21 cannot be secured. Conversely, if it is too small, the elasticity is too low and the member strength is poor. Since the reaction force of the toner supply roller 1 of this embodiment is 10 to 60 mN / mm, a sufficient nip width can be secured and the member strength is secured. It should be noted that the toner supply roller 1 of this embodiment is quite soft and cannot measure Asker hardness.

  Next, a method for manufacturing the toner supply roller 1 of this embodiment will be described. Polyether polyol was used as the polyol and toluene diphenyl diisocyanate was used as the isocyanate, and one or more of carbon black, ionic conductive agent, metal oxide and the like were mixed as the conductive agent. This mixture was placed in a mixing device for mixing air such as an Oaks mixer and mixed mechanically.

  As a result, the chemical foaming by the gas generated by the chemical reaction and the mechanical foaming by the air forcedly mixed by the mixer occur at the same time, and a foaming state in which many uniform fine bubbles are generated can be obtained. This was cured to produce urethane foam. This foamed urethane was processed into the shape of the toner supply roller 1. The toner supply roller 1 of the present embodiment thus obtained has a number of cells that can be measured by observing the surface thereof in the range of 30 to 80/25 mm.

  In this way, urethane foam having a large number of cells can be obtained by using both mechanical foaming and chemical foaming. Although chemical foaming alone can increase the content of air in the volume, the bubble diameter tends to increase. Therefore, the foam has a relatively thick cell wall. On the other hand, with mechanical foaming alone, it is difficult to increase the content of air in the volume, but bubbles with a small bubble diameter are produced. Therefore, a foam with a thin cell wall can be obtained. By using these together, it was possible to obtain urethane foam with a small number of cells and a large number of cells, while the total air volume was almost the same as the conventional one. Further, by adjusting the mixing ratio of polyol and isocyanate or the stirring time of the Oaks mixer, the toner supply roller 1 satisfying the reaction force characteristic range of this embodiment could be manufactured.

  Next, using multiple types of toner supply rollers with different characteristics, obtained by changing the mixing ratio of polyol and isocyanate, or the stirring time of Oaks mixer, it is possible to fix the toner in the apparatus or to cover the image with the background. The presence or absence of occurrence of toner and the amount of toner transported on the developing roller 21 were compared and evaluated. In particular, a comparison was made for the case where low-temperature fixing toner was used.

  The characteristics of the low-temperature fixing toner used for evaluation are a weight average particle diameter of 4.5 to 7.0 μm, endothermic peaks due to glass transition at two locations of 10 to 30 ° C. and 50 to 65 ° C., The softening point of the flow tester is 70 to 110 ° C. Here, the particle size is 4.5 μm, the endothermic peaks are 10 ° C. and 50 ° C., the softening point is 70 ° C. (hereinafter referred to as toner B), the particle size is 6.5 μm, and the endothermic peaks are 20 ° C. and 60 ° C. The one having a softening point of 100 ° C. (hereinafter referred to as toner C) was used.

  When such a low-temperature fixing toner is used, for example, a fixing temperature of about 160 ° C. is sufficient for roller fixing generally performed in a high-speed process in which the peripheral speed of the photoconductor 11 is about 300 mm / s. This is fixing at a considerably low temperature as compared with the case where the conventional toner requires about 200 ° C. For comparison, an evaluation experiment was also conducted on a toner that has been used conventionally and is not low-temperature fixing (hereinafter referred to as toner A). The endothermic peak of toner A is at one location between 55 and 65 ° C., and the softening point is 120 to 150 ° C.

  The toner characteristics described above were obtained by the following method. The particle size of the toner was measured using FPIA manufactured by SYSMEX. The endothermic peak was measured according to ASTM standard D3418-8. The softening point in the flow tester was measured under the following conditions using a flow tester CFT-500 manufactured by Shimadzu Corporation. The measurement conditions were as follows: toner pellets having a height of 10 mm were prepared, the heating rate was 6 ° C./min, the plunger pressure was 200 MPa, and the nozzle diameter was 1 mm. Then, the temperature at which the descending amount was 5 mm was taken as the softening point.

  The evaluation was performed by changing the toner supply roller of the developing device of the magiccolor 5440DL manufactured by KONICA MINOLTA to the ones of the examples and comparative examples, and incorporating the above-mentioned low-temperature fixing toner into the toner cartridge. Among these, Examples 1 to 6 are toner supply rollers that satisfy all the characteristic ranges of the present embodiment. Examples 7 to 10 are examples in which the conditions other than the developing device do not satisfy the range of the present embodiment, but the toner supply roller satisfies the characteristic range of the present embodiment.

  For example, in Examples 7 to 9, the peripheral speed of the photosensitive member is too small, but the toner supply roller satisfies the characteristic range of this embodiment. In Example 10, the above-described conventional toner is used, but the toner supply roller satisfies the characteristic range of this embodiment. On the other hand, Comparative Examples 1 to 6 are charging devices that do not satisfy the characteristic range of this embodiment. In Comparative Examples 1 to 4, the reaction force is too large. Comparative Examples 1, 2, and 5 are manufactured by impregnating after foaming instead of mixing the conductive agent into the material. Comparative Examples 6-7 have too many cells.

The evaluation criteria were as follows.
About toner fixation: When there is no toner fixation inside the developing device ○
When there is toner stuck inside the developing device ×
For background fogging: ○
If it can be confirmed visually ×
Regarding toner transport amount: ○ in the range of 5 to 7 g / m ²
X otherwise
Comprehensive evaluation: ○ When all of toner adhesion, background fog, and toner transport amount are ○
X if any are x

  In this evaluation test, an experiment was performed in an NN environment (temperature 23 degrees, humidity 65%) and an HH environment (temperature 30 ° C., humidity 90%). In each environmental condition, an experiment was performed with the charging device being new and after printing 10,000 sheets of a 5% chart. And only when the criteria were satisfied in all of these conditions, it was marked as “◯”.

  The results of the evaluation experiment are as shown in Table 1. All of Examples 1 to 6 were good results. Moreover, the result of Examples 7-10 was also favorable. That is, the toner supply roller 1 of the present embodiment is effective for an image forming apparatus that employs a low-temperature fixing toner, which is a high-speed process, and has no problem even with a conventional low-speed image forming apparatus or an apparatus that uses toner that is not low-temperature fixing. It was confirmed that it could be used.

  As described above in detail, in the present embodiment, a disk-like pressure member having a surface number of cells in the range of 30 to 80/25 mm and a diameter of 50 mm is used as the toner supply roller 1. The reaction force in the direction of the pushing axis when pushed to 30% is in the range of 10 to 60 mN / mm. Therefore, a sufficient nip can be obtained with a small pressing force, and the restoration after exiting from the nip is fast. That is, the toner supply roller is manufactured using chemical foaming, and has stable conductivity and low hardness over a long period of time.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, members other than the toner supply roller of the image forming apparatus are not limited to those shown in the drawings, and any members may be used. The present invention is applicable to any image forming apparatus such as a color or monochrome printer, a copier, and a FAX.

1 is a schematic configuration diagram illustrating an image forming apparatus according to the present embodiment. FIG. 6 is a cross-sectional view illustrating a toner supply roller of the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Toner supply roller 2 Core metal 3 Elastic body layer 10 Image forming apparatus 11 Photoconductor 12 Developing apparatus

Claims (3)

In a toner supply roller having a cored bar and a cylindrical foamed elastic layer and supplying toner to a developing roller of an image forming apparatus,
The foamed elastic layer is a conductive layer formed by foaming a material mixed with a conductive material component in advance,
The number of cells measured by observing the surface of the foamed elastic layer is in the range of 30-80 / 25 mm;
The reaction force per unit length in the indentation axial direction when the foamed elastic layer is pushed from the outside to 30% of its thickness in the radial direction using a disk-like pressure member of φ50 mm is 10 to 60 mN. A toner supply roller in a range of / mm. In the image forming apparatus, comprising: a photosensitive member; a developing roller; and a toner supplying roller that supplies toner to the developing roller, wherein the toner supplying roller includes a metal core and a cylindrical foamed elastic layer. Toner supply roller
The foamed elastic layer is a conductive layer formed by foaming a material mixed with a conductive material component in advance,
The number of cells measured by observing the surface of the foamed elastic layer is in the range of 30-80 / 25 mm;
The reaction force per unit length in the indentation axial direction when the foamed elastic layer is pushed from the outside to 30% of its thickness in the radial direction using a disk-like pressure member of φ50 mm is 10 to 60 mN. An image forming apparatus characterized by being in the range of / mm. The image forming apparatus according to claim 2,
The rotational speed of the image carrier is a peripheral speed of 200 mm / sec or more;
The toner supplied by the toner supply roller is
The weight average particle size is in the range of 4.5 to 7.0 μm;
There are two endothermic peaks due to glass transition in the range of 10-30 ° C. and 50-65 ° C.,
An image forming apparatus having a softening point in a range of 70 to 110 ° C.

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