JP5309913B2 - Toner supply roller, developing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a memory image and filming of a developing roller from occurring while suppressing heat generation and stress applied to toner and the developing roller at a nip part between the developing roller and a supply roller. <P>SOLUTION: The developing device 34 includes the developing roller 48 which develops an electrostatic latent image formed on an outer peripheral surface of an electrostatic latent image carrier 12 to be a visible image by attaching toner 68 to the electrostatic latent image, and the toner supply roller 52 which supplies and collects the toner 68 between the developing roller 48 and the toner supply roller 52, wherein the developing roller 48 and the toner supply roller 52 are arranged to rotate so as to move in the same direction at their contact part. As for a polyurethane foam layer 56 of the toner supply roller 52 used in the developing device 34, the number of cells thereof per inch is 30 or more and 80 or less, and an open ratio of a wall surface of cells thereof is 3% or more and 50% or less. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus, a developing device used in the image forming apparatus, and a toner supply roller used in the developing device.

  An electrophotographic image forming apparatus has an electrostatic latent image carrier that carries an electrostatic latent image, and the electrostatic latent image is visualized by toner supplied from a developing device. A toner image is formed on the carrier. The toner image formed on the electrostatic latent image carrier is transferred to a recording sheet such as paper directly or via an intermediate transfer member. The recording sheet to which the toner image has been transferred is heated and pressurized by a fixing device, whereby the toner image is fixed on the recording sheet.

  The developing device includes a developing roller disposed opposite to the electrostatic latent image carrier and a supply roller that supplies and collects toner between the developing roller. The rotation direction of the developing roller and the supply roller can be arbitrarily set. However, when the rollers rotate so as to move in opposite directions (so-called counter direction) at the contact portion (nip portion) between the developing roller and the supply roller, A lot of toner can be supplied and collected.

  As for the supply roller, a technique using polyurethane foam as a material for the surface layer has been proposed (Patent Document 1). According to this technology, due to the excellent flexibility of the polyurethane foam, the stress applied to the toner at the nip portion between the supply roller and the developing roller can be reduced, and the deterioration of the toner can be suppressed.

  On the other hand, in recent years, reduction of the fixing temperature (heating temperature of the fixing device) has been further demanded from the viewpoint of speeding up the image forming process and consideration of environmental problems. In order to reduce the fixing temperature, it is necessary to use a toner capable of fixing at a low temperature (low-temperature fixing toner).

  However, in order to increase the speed of the image forming process, it is necessary to rotate the developing roller and the supply roller at a high speed. Therefore, a large frictional force acting between the developing roller and the supply roller causes the development roller and the supply roller to rotate. While generating heat in the nip portion, stress applied to the toner and the developing roller increases. For this reason, when low-temperature fixing toner is used in a high-speed process image forming apparatus, toner melting, fogging due to toner degradation (a phenomenon in which toner adheres to a non-image portion of a sheet), development roller wear, and development roller wear Filming (a phenomenon in which a film is generated on the roller surface) may occur.

  In order to solve such a problem, the developing roller and the supply roller are rotated so as to move in the same direction (so-called “wiz direction”) at the nip portion, thereby acting between the developing roller and the supply roller. It is conceivable to reduce the friction force.

JP 2007-145904 A

  However, when the rotation direction of the developing roller and the supply roller is set to the width direction, the force that scrapes the toner on the developing roller by the supply roller becomes small, and the amount of toner collected by the supply roller may be insufficient. For this reason, a memory image (an image appearing due to toner that could not be collected by the supply roller remaining on the developing roller) or filming of the developing roller may occur.

  SUMMARY OF THE INVENTION An object of the present invention is to prevent the occurrence of filming of a memory image and a developing roller while suppressing heat generation at a nip portion between the developing roller and a supply roller and stress applied to the toner and the developing roller.

In order to solve the above problems, a developing device according to the present invention provides:
Development that makes the electrostatic latent image visible by attaching toner to the electrostatic latent image formed on the outer peripheral surface of the electrostatic latent image carrier and disposed opposite to the outer peripheral surface of the electrostatic latent image carrier. Laura,
A toner supply roller that is rotationally driven while being in contact with the outer peripheral surface of the developing roller, and that supplies and collects toner with the developing roller at the contact portion;
And the developing roller and the toner supply roller, a placed developing equipment to rotate so as to move in the same direction at their contact portion,
The toner supply roller has a cored bar and a polyurethane foam layer covering the outer peripheral surface of the cored bar,
The polyurethane foam layer has 30 to 80 cells per inch,
The opening ratio of the wall surface of the cell of the polyurethane foam layer is 3% or more and 50% or less ,
The polyurethane foam layer has a load per unit length received by the pressing surface of 1 gf / mm or more when the pressing surface is pressed into a predetermined pressing surface to a depth of 30% of the thickness of the polyurethane foam layer. 6 gf / mm or less,
The density of the polyurethane foam layer is 0.03 g / cm ³ or more and 0.2 g / cm ³ or less,
The volume resistivity of the polyurethane foam layer is 10 ² Ωcm or more and 10 ⁶ Ωcm or less,
The amount of penetration of the polyurethane foam layer into the developing roller is 5% or more and 40% or less of the thickness of the polyurethane foam layer,
The contact nip width between the supply roller and the development roller in the circumferential direction of the supply roller is 3 mm or more and 6 mm or less,
The peripheral speed of the developing roller is 300 mm / s or more and 600 mm / s or less,
A regulating member for regulating the layer thickness of the toner on the developing roller is disposed in contact with or close to the outer peripheral surface of the developing roller at a position lower than the contact portion between the developing roller and the toner supply roller;
A toner having a capsule structure including an inner material and an outer shell covering the inner material;
The toner has an endothermic peak at the time of glass transition measured by differential scanning calorimetry (DSC) having a first peak of 10 to 30 ° C. and a second peak of 50 to 65 ° C. ,
The softening point of the toner measured by a flow tester is 70 ° C. or higher and 110 ° C. or lower .

  Furthermore, an image forming apparatus according to the present invention includes the above-described developing device.

  According to the present invention, since the number of cells of the polyurethane foam layer of the toner supply roller is 30 / inch or more, a large number of cells can be brought into contact with the toner at the nip portion between the supply roller and the developing roller. Further, the number of cells of the polyurethane foam layer is 80 / inch or less, and each cell has a certain size, so that the toner is hardly clogged with the cell. Furthermore, the opening ratio of the cell wall surface of the polyurethane foam layer is set to 3% or more and 50% or less, whereby the structure of the polyurethane foam layer becomes an open cell structure close to the closed cell structure. Therefore, more toner can be taken into the interior than a polyurethane foam layer having a general closed cell structure, and toner aggregation is less likely to occur in the interior as compared with a general open cell structure. Therefore, even when the developing roller and the supply roller are rotated in the so-called “wiz” direction, the toner recovery performance of the supply roller can be sufficiently secured, and the toner recovery performance can be maintained well over a long period of time. Therefore, by rotating the developing roller and the supply roller in the width direction, the supply roller is controlled by the above properties of the polyurethane foam layer while suppressing heat generation at the nip portion between the developing roller and the supply roller and stress applied to the toner and the development roller. By improving the toner collecting performance, it is possible to prevent filming of the memory image and the developing roller.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In the following description, terms indicating a specific direction (for example, “up”, “down”, “left”, “right”, and other terms including them, “clockwise direction”, “counterclockwise” ”) Is used to facilitate understanding of the invention with reference to the drawings, and the present invention should not be construed as being limited by the meaning of these terms.

[1. Image forming apparatus]
FIG. 1 shows a portion related to image formation of an electrophotographic image forming apparatus according to the present invention. The image forming apparatus may be any of a copier, a printer, a facsimile machine, and a multi-function machine having a combination of these functions. The image forming apparatus 1 includes a photoreceptor 12 that is an electrostatic latent image carrier. In the embodiment, the photoconductor 12 is formed of a cylindrical body, but the present invention is not limited to such a form, and an endless belt type photoconductor can be used instead. The photoreceptor 12 is drivingly connected to a motor (not shown), and is rotated in the direction of arrow 14 based on the driving of the motor. Around the photoconductor 12, a charging station 16, an exposure station 18, a developing station 20, a transfer station 22, and a cleaning station 24 are arranged along the rotation direction of the photoconductor 12.

  The charging station 16 includes a charging device 26 that charges a photosensitive layer, which is the outer peripheral surface of the photosensitive member 12, to a predetermined potential. In the embodiment, the charging device 26 is represented as a cylindrical roller. However, instead of this, other types of charging devices (for example, a rotary or fixed brush-type charging device or a wire-discharge-type charging device) may be used. Can be used. In the exposure station 18, the image light 30 emitted from the exposure device 28 disposed in the vicinity of the photosensitive member 12 or away from the photosensitive member 12 travels toward the outer peripheral surface of the charged photosensitive member 12. A passage 32 is provided. On the outer peripheral surface of the photoconductor 12 that has passed through the exposure station 18, an electrostatic latent image is formed that includes a portion where the image light is projected and the potential is attenuated and a portion where the charged potential is substantially maintained. In the embodiment, the portion where the potential is attenuated is the electrostatic latent image portion, and the portion where the charged potential is substantially maintained is the electrostatic latent image non-image portion. The developing station 20 includes a developing device 34 that visualizes the electrostatic latent image using a powder developer. The detailed configuration of the developing device 34 will be described later. The transfer station 22 includes a transfer device 36 that transfers a visible image formed on the outer peripheral surface of the photoreceptor 12 to a sheet 38 such as paper or film. In the embodiment, the transfer device 36 is represented as a cylindrical roller, but other types of transfer devices (for example, wire discharge transfer devices) can also be used. The cleaning station 24 includes a cleaning device 40 that collects untransferred toner remaining on the outer peripheral surface of the photoconductor 12 without being transferred to the sheet 38 at the transfer station 22 from the outer peripheral surface of the photoconductor 12. In the embodiment, the cleaning device 40 is shown as a plate-like blade, but other types of cleaning devices (for example, a rotary type or a fixed type brush type cleaning device) may be used instead.

  When the image forming apparatus 1 having such a configuration forms an image, the photoconductor 12 rotates clockwise based on the driving of a motor (not shown). At this time, the outer peripheral portion of the photoreceptor passing through the charging station 16 is charged to a predetermined potential by the charging device 26. The charged outer periphery of the photoconductor is exposed to image light 30 at an exposure station 18 to form an electrostatic latent image. The electrostatic latent image is conveyed to the developing station 20 along with the rotation of the photosensitive member 12, where it is visualized as a developer image by the developing device 34. The visualized developer image is conveyed to the transfer station 22 along with the rotation of the photosensitive member 12, and is transferred to the sheet 38 by the transfer device 36 there. The sheet 38 to which the developer image has been transferred is conveyed to a fixing station (not shown), where the developer image is fixed to the sheet 38. The outer peripheral portion of the photosensitive member that has passed through the transfer station 22 is conveyed to the cleaning station 24 where the developer remaining on the outer peripheral surface of the photosensitive member 12 without being transferred to the sheet 38 is recovered.

[2. Development device]
The developing device 34 includes a housing 42 that houses a developer and various members described below. In order to facilitate understanding of the invention by simplifying the drawings, a part of the housing 42 is omitted.

  The housing 42 is provided with an opening 44 opened toward the photosensitive member 12, and a developing roller 48 is provided in a space 46 formed in the vicinity of the opening 44. The developing roller 48 is disposed to face the outer peripheral surface of the photoconductor 12 through a predetermined developing gap 50. The developing roller 48 is disposed in parallel with the photoconductor 12. The developing roller 48 is drivingly connected to a motor (not shown) and is rotated in the direction of an arrow 78 based on the driving of the motor. From the viewpoint of speeding up the image forming process, the peripheral speed of the developing roller 48 is preferably set to 300 mm / s or more and 600 mm / s or less. A power supply (not shown) for forming a predetermined electric field between the photosensitive member 12 and the developing roller 48 is connected to the developing roller 48.

  As the developing roller 48, for example, a metal roller is used. In this case, it is preferable to oxidize the surface of the metal roller. However, as the material of the metal roller 48, a material other than metal can be used. For example, an elastic material having conductivity may be used. Specific examples of the elastic material used for the developing roller 48 include rubber or polyurethane foam. By making the elastic material contain carbon, metal powder, ionic conductive material, or the like, the developing roller 48 has conductivity. Is granted. When an elastic material is used as the material of the developing roller 48, a coating layer made of a resin having excellent releasability such as fluorine may be provided on the surface of the roller. Further, unevenness for controlling the thickness of the toner layer may be provided on the surface of the developing roller 48 made of an elastic material by dispersing resin beads or inorganic powder.

  Behind the developing roller 48, a supply roller 52 is disposed in contact with the outer peripheral surface of the developing roller 48. The supply roller 52 includes a cored bar 54 and a polyurethane foam layer 56 that covers the outer peripheral surface of the cored bar 54. The specific configuration of the polyurethane foam layer 56 will be described in detail later.

The supply roller 52 is arranged in parallel to the developing roller 48 and rotatable. The supply roller 52 is drivingly connected to a motor (not shown) and is rotated in the direction of arrow 80 based on the driving of the motor. Accordingly, the supply roller 52 and the developing roller 48 rotate so as to move in the same direction at the contact portion (nip portion) 66 thereof. The peripheral speed of the supply roller 52 is determined according to the peripheral speed of the developing roller 48. Specifically, the ratio R (V _S / V _D ) of the peripheral speed V _S of the supply roller 52 to the peripheral speed V _D of the developing roller 48 is set to be 0.5 or more and 3.0 or less, for example. The supply roller 52 may be driven by the developing roller 48 without being connected to the motor. In this case, the circumferential speed ratio R (V _S / V _D ) is 1.0.

  The supply roller 52 is preferably arranged so that the contact nip width between the supply roller 52 and the developing roller 48 is 3 mm or more and 6 mm or less in the circumferential direction. By setting the contact nip width to 3 mm or more, the scraping force of the toner 68 on the developing roller 48 by the supply roller 52 can be sufficiently secured. Further, by setting the contact nip width to 6 mm or less, heat generation at the nip portion 66 between the supply roller 52 and the developing roller 48 and stress of the toner 68 can be suppressed.

  The amount of the polyurethane foam layer 56 biting into the developing roller 48 is preferably 5% to 40% of the thickness of the polyurethane foam layer 56.

  The supply roller 52 may be connected to a power source (not shown) for forming an electric field between the developing roller 48 and the supply roller 52.

  A regulating member 60 is disposed in contact with the outer peripheral surface of the developing roller 48 on the downstream side of the nip 66 with the supply roller 52 in the rotation direction of the developing roller 48. However, the regulating member 60 may be disposed close to the outer peripheral surface of the developing roller 48 with a slight gap. The restricting member 60 is disposed at a position lower than the nip portion 66 between the developing roller 48 and the supply roller 52, and the toner easily enters the restricting portion entrance located in the lower direction by gravity, resulting in poor supply. The effect that it is hard to produce problems, such as these, is acquired. The toner 68 on the developing roller 48 passing through the nip portion between the developing roller 48 and the regulating member 60 is charged by frictional contact with the regulating member 60 and the layer thickness of the toner 68 is regulated. On the upstream side of the nip portion 66 with the supply roller 52 in the rotation direction of the developing roller 48, a static eliminating member 62 is disposed in contact with the outer peripheral surface of the developing roller 48. The toner 68 on the developing roller 48 passing through the nip portion between the developing roller 48 and the charge removing member 62 is discharged by contacting the charge removing member 62.

  Behind the space 46, a toner storage unit 50 for storing toner is disposed. A stirring member 64 is provided in the toner storage unit 50 so as to be rotatable in the direction of an arrow 82. When the stirring member 64 rotates, the toner stored in the toner storage unit 50 is appropriately supplied to the space 46 while being stirred.

  For the developing device 34, a one-component developer is used. As the toner 68 constituting the developer, it is preferable to use a toner that can be fixed at a low temperature (low-temperature fixing toner), whereby the fixing temperature can be reduced. Therefore, the time required for heating the fixing device can be shortened, and the image forming process can be accelerated. Further, as the toner 68, it is preferable to use a toner having a capsule structure composed of an internal material and an outer shell covering the internal material. In this case, a material having a low melting point and a glass transition point is used for the internal material so as to facilitate fixing at low temperature, and the outer shell has an internal so as to improve heat resistance during storage or distribution. A material having a higher melting point and glass transition point than the material is used. In this case, the endothermic peaks at the time of glass transition of the toner 68 measured by differential scanning calorimetry (DSC) are the first peak (glass transition point of the internal material) and the second peak (glass transition of the outer shell). Point). The first peak is preferably 10 ° C. or higher and 30 ° C. or lower, and the second peak is preferably 50 ° C. or higher and 65 ° C. or lower. The softening point of the toner 68 measured by a flow tester is preferably 70 ° C. or higher and 110 ° C. or lower. Further, in this case, it is preferable that the internal material contains a larger amount of release agent than the conventional pulverized toner.

  The operation of the developing device 34 configured as described above will be described. During image formation, the developing roller 48 and the supply roller 52 rotate in the directions of arrows 78 and 80, respectively, based on driving of a motor (not shown). The toner 68 carried on the supply roller 52 is conveyed to the nip portion 66 with the developing roller 48 by the rotation of the supply roller 52, and developed while being charged by frictional contact between the developing roller 48 and the supply roller 52 in the nip portion 66. Supplied to roller 48. When the toner 68 on the developing roller 48 supplied from the supply roller 52 is conveyed to the nip portion with the regulating member 60 by the rotation of the developing roller 48, the toner 68 is frictionally charged and the layer thickness is regulated by the regulating member 60. The Further, the toner 68 on the developing roller 48 conveyed to the opposite portion of the photoconductor 12 by the rotation of the developing roller 48 is subjected to the action of an electric field formed between the developing roller 48 and the photoconductor 12, so that the photoconductor 12. Move to the electrostatic latent image portion on the outer peripheral surface of the substrate, whereby the electrostatic latent image is visualized. The toner 68 remaining on the outer peripheral surface of the developing roller 48 after passing through the portion facing the photoreceptor 12 is conveyed to the nip portion with the neutralizing member 62 by the rotation of the developing roller 48 and is neutralized by the neutralizing member 62. Then, it is conveyed again to the nip portion 66 with the supply roller 52. The toner on the developing roller 48 conveyed to the nip 66 with the supply roller 52 is mechanically scraped off from the outer peripheral surface of the developing roller 48 by the supply roller 52.

[3. (Polyurethane foam layer of supply roller)
The opening ratio of the cell wall surface of the polyurethane foam layer 56 is 3% or more and 50% or less. The opening ratio is higher than the opening ratio (about 1%) of a polyurethane foam having a general closed cell structure manufactured by a known mechanical floss method or the like, and is generally manufactured by a known chemical foaming method or the like. It is lower than the open area ratio (about 60%) of polyurethane foam having an open cell structure. That is, the polyurethane foam layer 56 has an open cell structure close to a closed cell structure. Therefore, more toner can be taken into the interior than a polyurethane foam layer having a general closed cell structure, and toner aggregation is less likely to occur in the interior as compared with a general open cell structure. Therefore, the toner collecting performance of the supply roller 52 can be sufficiently secured, and the toner collecting performance can be maintained well over a long period of time.

  In addition, the polyurethane foam layer 56 has 30 to 80 cells per inch. This number of cells is less than the number of cells of a general closed-cell structure polyurethane foam (about 100 cells / inch) and more than the number of cells of a general open-cell structure polyurethane foam (25 cells / inch). . That is, the polyurethane foam layer 56 can bring a larger number of cells into contact with the toner at the nip portion 66 between the supply roller and the developing roller than a polyurethane foam having a general open cell structure. Further, since each cell of the polyurethane foam layer 56 is larger than a polyurethane foam having a general closed cell structure, it is difficult for toner to be clogged in each cell.

  The polyurethane foam layer 56 has a hardness as low as that of a general open cell structure. In the present specification, the hardness of the polyurethane foam layer 56 is determined so that the polyurethane foam layer 56 is pressed to a depth corresponding to 30% of the surface side of the thickness (until the thickness of the polyurethane foam layer 56 becomes 70% of the original). It is represented by the magnitude of the load per unit length that the pressing surface receives when it is pushed into the contacting surface. Specifically, the hardness of the polyurethane foam layer 56 is preferably 1 gf / mm or more and 6 gf / mm or less. This hardness is smaller than the hardness when the polyurethane foam layer has a general closed cell structure (about 8.5 gf / mm), and the hardness when the polyurethane foam layer has a general open cell structure (0.8 gf). / Mm). That is, since the polyurethane foam layer 56 has the same degree of flexibility as a general open-cell structure polyurethane foam layer, the developing roller 48 and the supply roller 52 are compared with a general closed-cell structure polyurethane foam layer. The stress of the toner 68 in the nip portion 66 can be reduced, and the deterioration of the toner 68 can be suppressed.

  Furthermore, the average value of the cell diameter of the polyurethane foam layer 56 is preferably 100 μm or more and 500 μm or less. The average value of the cell diameter is smaller than the cell diameter (about 700 μm) of a general open-cell structure polyurethane foam layer, and larger than the cell diameter (about 80 μm) of a general closed-cell structure polyurethane foam layer. . That is, the polyurethane foam layer 56 has finer cells than a general open-cell structure polyurethane foam layer, and therefore has a toner scraping performance superior to a general open-cell structure polyurethane foam layer.

Furthermore, the polyurethane foam layer 56 has a lower density than a polyurethane foam layer having a general closed cell structure. Specifically, the density of the polyurethane foam layer 56 is preferably 0.03 g / cm ³ or more and 0.2 g / cm ³ or less. Thereby, the flexibility of the polyurethane foam layer 56 is sufficiently secured, and the stress of the toner 68 in the nip portion 66 between the supply roller 52 and the developing roller 48 can be suppressed.

The volume resistivity of the polyurethane foam layer 56 is preferably 10 ² Ωcm or more and 10 ⁶ Ωcm or less. Thereby, the polyurethane foam layer 56 has appropriate conductivity, and an appropriate electric field can be formed between the supply roller 52 and the developing roller 48.

[4. (Polyurethane foam production method)
With respect to the polyurethane foam layer 56 having the above configuration, a method for producing a polyurethane foam as a material thereof will be described.

  The polyurethane foam used in the present invention is produced by a method combining a known mechanical flossing method and a known chemical foaming method.

  The mechanical flossing method and the chemical foaming method are common in that foaming is performed by mixing a polyol and an isocyanate. However, in the mechanical froth method, a foaming agent is not used as a raw material, and physical foaming is performed by mixing a gas for forming bubbles such as an inert gas, whereas in a chemical foaming method, a raw material is used. The difference is that a foaming agent is used and chemical foaming is performed by a chemical reaction between the isocyanate and the foaming agent. When the mechanical floss method is employed, a polyurethane foam having a homogeneous closed cell structure can be produced, but it is difficult to produce a polyurethane foam having an open cell structure having a low density. On the other hand, when the chemical foaming method is employed, a low-density open-cell structure polyurethane foam can be easily produced, but it is difficult to produce a homogeneous closed-cell structure polyurethane foam.

  In contrast to these conventional manufacturing methods, the polyurethane foam manufacturing method used in the present invention is used in the chemical foaming method in addition to the polyol, isocyanate and gas for forming bubbles used in the mechanical floss method. A foaming agent is used as a raw material, which combines physical foaming due to the incorporation of gas for forming bubbles and chemical foaming associated with the chemical reaction of the isocyanate and the foaming agent. Therefore, homogeneous cells formed by physical foaming are joined together by chemical foaming, and a homogeneous and low density polyurethane foam, that is, a polyurethane foam having an open cell structure close to a closed cell structure can be produced. Hereinafter, a specific manufacturing method will be described.

  The polyurethane foam used in the present invention is produced from the beginning through a raw material adjustment step, a mixing step, and a heating step.

  In the raw material adjusting step, each raw material used for manufacturing the polyurethane foam is adjusted. As raw materials, secondary materials such as polyol, isocyanate, gas for forming bubbles such as inert gas, foaming agent, and catalyst are used.

  As a polyol, the well-known polyol which has an active hydrogen group is used individually or in combination of 2 or more types, for example. Specifically, examples of the polyol used include polyether polyol, polyester polyol, polycarbonate polyol, and polydiene-based polyol. As the isocyanate, for example, a well-known aromatic system such as toluene diphenyl diisocyanate (TDI), TDI prepolymer, methylene diphenyl diisocyanate (MDI), crude MDI, polymeric MDI, uretdione-modified MDI, or carbodiimide-modified MDI, aliphatic or aliphatic Various polyisocyanates such as ring systems are used. For example, nitrogen is used as the gas for forming bubbles. As the foaming agent, a raw material that generates a gas by a chemical reaction with isocyanate is used, and specifically, water or the like is used. The blowing agent is mixed with the polyol in advance before the mixing step. As the catalyst, for example, an amine catalyst and an organic acid salt catalyst are used. Amine-based catalysts are mainly used to promote rapid chemical foaming, and organic acid salt-based catalysts are mainly used to cure the polyurethane foam backbone. As the organic acid salt catalyst, it is preferable to use a heat-sensitive catalyst that exhibits a catalytic effect by required heating. Thereby, the hardening of the skeleton of the polyurethane foam can be delayed more than the chemical foaming carried by the amine-based catalyst, and chemical foaming can surely occur.

  Factors that determine the hardness of the polyurethane foam include, for example, the type of polyol and the isocyanate index. In the present specification, the isocyanate index refers to a percentage of the ratio N / M of the number of moles of isocyanate groups in isocyanate to the total number of moles M of hydroxyl groups of the blowing agent and hydroxyl groups of the polyol. In order to form the polyurethane foam to have the above-mentioned desired hardness, for example, a polyether polyol or a polyester polyol having a molecular weight of 1000 to 6000 and a functional group number of 2 to 5 is preferably used as the polyol. It is preferable to adjust the isocyanate index to 90 to 110.

  When water is used as a foaming agent, when each raw material is mixed, carbon dioxide is generated by a chemical reaction between water and isocyanate, thereby forming bubbles (cells). In order to form a low-density polyurethane foam having fine cells, carbon dioxide generated by a chemical reaction between water and isocyanate is placed inside the bubbles (cells) physically generated by the gas for forming bubbles. Need to get in. In order to achieve this object, it is preferable to adjust the mixing amount of water to 0.3 to 1.5 parts by mass with respect to 100 parts by mass of the polyol.

  In the mixing step, a polyol, an isocyanate, a gas for forming bubbles, a catalyst, and the like mixed with a foaming agent such as water are mixed. As a result, first, physical foaming occurs, and homogeneous bubbles (cells) having a bubble-forming gas as a nucleus are formed. Then, a gas such as carbon dioxide is generated by causing a chemical reaction between the blowing agent contained in the polyol and the isocyanate, and this gas enters the cell formed by physical foaming, and the cell diameter as a whole. Increases and the cells are connected. Thereby, a cell having a large diameter is formed while being homogeneous.

  In the heating step, the mixed raw material is heated to accelerate the resinification reaction and cure the polyurethane foam skeleton. The heating temperature and heating time in the heating step are appropriately determined according to the raw material of the polyurethane foam in accordance with a known mechanical flossing method.

  According to the manufacturing method demonstrated above, the polyurethane foam with a high opening rate of a cell wall surface is formed compared with the polyurethane foam manufactured by the mechanical floss method. For this reason, when the polyurethane foam is impregnated with a solution containing a conductive substance or the like, the solution easily penetrates into the polyurethane foam, so that a function such as conductivity can be easily imparted.

  The polyurethane foam manufactured in this way is processed into a desired shape and fixed to a cored bar, whereby the toner supply roller 52 is manufactured. If necessary, before fixing the metal core to the polyurethane foam, a step of impregnating the polyurethane foam into a solution containing a conductive substance and the like and a step of drying the polyurethane foam after impregnating the solution are provided. May be.

  While the present invention has been described with reference to the above-described embodiments, the present invention is not limited to the above-described embodiments. For example, in the present invention, the method for producing the polyurethane foam layer is not necessarily limited to the above-described embodiment, and does not prevent the polyurethane foam layer from being produced by another method.

(Test 1)
When a low-temperature fixing toner is used in an image forming apparatus for a high-speed process, a test was conducted to confirm process conditions suitable for preventing toner aggregation and melting inside the developing device. Specifically, as the process conditions, the ratio of the peripheral velocity V _S of the supply roller to the circumferential speed V _D of the developing roller _{R (V S / V D)} , the suitable size of the contact pressure of the supply roller to the developing roller confirmed.

  As the image forming apparatus, an image forming apparatus of Magiccolor 5570 manufactured by Konica Minolta was used, and as a developing apparatus mounted on the image forming apparatus, an apparatus obtained by appropriately modifying the developing apparatus of Magiccolor 5570 manufactured by Konica Minolta was used. . As the low-temperature fixing toner, toner a and toner b having the capsule structure as described above were used. The toner a has a first endothermic peak (glass transition point of an internal material) at the time of glass transition measured by differential scanning calorimetry (DSC) of 10 ° C., and a second endothermic peak (glass transition point of the outer shell). ) Is 50 ° C., and the softening point measured by a flow tester is 70 ° C. The toner b has a first endothermic peak (glass transition point of the internal material) at the time of glass transition measured by differential scanning calorimetry (DSC) of 30 ° C., and a second endothermic peak (glass transition point of the outer shell). ) Is 65 ° C., and the softening point measured by a flow tester is 110 ° C. As the material of the supply roller, a polyurethane foam having 35 cells per inch, a cell wall opening ratio of 55%, and a roller hardness of 6.5 gf / mm was used.

As shown in Table 1, when the peripheral speed of the developing roller was set to 600 mm / s and the toner a was used, the peripheral speed ratio R (V _S / V _D ) and the rotation direction of the supply roller were varied. Examples 1-1 to 1-8 were set. Similarly, Experimental Example 2-1 to Experimental Example 2-8 were set for the case where the peripheral speed of the developing roller was set to 450 mm / s and the toner a was used. Similarly, Experimental Example 3-1 to Experimental Example 3-8 were set for the case where the peripheral speed of the developing roller was set to 300 mm / s and the toner b was used. The peripheral speed ratio R (V _S / V _D ) was adjusted by changing the peripheral speed of the supply roller. In addition, the description “driven” in the rotation direction column of Table 1 means that the supply roller is driven to rotate by the developing roller, and “driven” and “with” indicate the same rotational direction.

  In order to evaluate the toner melting prevention performance for each experimental example, a blank sheet is used for each experimental example using the above-described image forming apparatus in a high-temperature and high-humidity environment (atmosphere temperature 30 ° C., relative humidity 85%) where heat generation is likely to occur. 100,000 images were continuously printed, and after completion of continuous printing, the toner in the developing device was melted and the surface of the supply roller was visually observed. Further, in order to evaluate the toner recovery performance of the supply roller for each experimental example, the above-described image forming apparatus is used for each experimental example in a low-temperature and low-humidity environment (atmosphere temperature 10 ° C., relative humidity 15%) in which memory defects are likely to occur. Then, 100,000 blank images were continuously printed, and the presence of fogging was confirmed every 10,000 sheets during continuous printing, and the memory image confirmation image was printed to confirm the occurrence of memory images. . Further, the presence or absence of contamination (filming) of the developing roller in this continuous printing was confirmed visually. The evaluation regarding the fogging and the memory image is “×” for those that occurred from the initial stage of continuous printing, “△” for those that occurred at the end of 10,000-sheet printing, and “○” for those that occurred at the end of 50,000-sheet printing. Those that did not occur even after printing more than 50,000 sheets are indicated by “◎”, and the evaluation regarding the contamination of the developing roller is “x”, and 30,000 that the developing roller has filmed up to 10,000 sheets printed. “△” indicates what occurred before the printing of the sheets, “◯” indicates that it occurred before the printing of 50,000 sheets, and “◎” indicates that it did not occur even after printing more than 50,000 sheets (see Table 1). . In these evaluations, “◯” and “◎” are accepted criteria.

  From the evaluation results on melting of the toner shown in Table 1, in Example 1-6 to Example 1-8, Example 2-6 to Example 2-8 and Example 3-6 to Example 3-8, the toner The supply roller was damaged due to melting of the roller. This is considered to be due to the heat generated in the nip portion between the developing roller and the supply roller. In the experimental example in which the supply roller was damaged due to melting of the toner, the supply roller was set to rotate in a so-called counter direction with respect to the developing roller, and in the other experimental examples, the supply roller was set with respect to the developing roller. It is set to rotate in a so-called with direction. For this reason, when using low-temperature fixing toner when the peripheral speed of the developing roller is set to a high speed (300 to 600 mm / s), melting of the toner inside the developing device and damage to the supply roller due to this are prevented. In order to achieve this, it has been confirmed that it is preferable to set the supply roller so as to rotate in the width direction with respect to the developing roller. However, in Experimental Examples 1-1 to 1-5, Experimental Examples 2-1 to 2-5, and Experimental Examples 3-1 to 3-5 in which the supply roller is set to rotate in the width direction with respect to the developing roller, A memory image was generated, and the contamination of the developing roller was at a level causing a problem in image quality. The memory image is generated because the residual toner on the developing roller is not sufficiently collected by the supply roller and remains on the developing roller until the next development. On the other hand, the contamination of the developing roller is caused by the toner remaining on the developing roller without being collected by the supply roller being repeatedly subjected to stress, so that the external additive of the toner adheres to the outer peripheral surface of the developing roller. it is conceivable that. As a result, it is necessary to develop a supply roller that exhibits sufficient toner recovery performance even when low-temperature fixing toner is used in an image forming apparatus for a high-speed process and the developing roller and the supply roller are rotated in the so-called with direction. It turns out that.

(Test 2)
When using a high-speed image forming device and setting the supply roller to rotate in the so-called “wiz” direction with respect to the developing roller, when using low-temperature fixing toner, confirm the suitable physical properties of the polyurethane foam layer of the supply roller A test was conducted. Specifically, as the physical properties of the polyurethane foam layer, suitable values for the number of cells, the cell wall opening ratio, hardness, density, and volume resistivity were confirmed.

  As the image forming apparatus, an image forming apparatus of Magiccolor 5570 manufactured by Konica Minolta was used, and as a developing apparatus mounted on the image forming apparatus, an apparatus obtained by appropriately modifying the developing apparatus of Magiccolor 5570 manufactured by Konica Minolta was used. .

  As the polyurethane foam layer of the supply roller attached to the developing device, one made of any one of the materials A to L shown in Table 2 was used. These materials A to L were produced by the method described in the above embodiment using polyol, isocyanate, amine-based catalyst, organic acid salt-based catalyst, water (foaming agent) and foam stabilizer as raw materials. Specifically, polyether polyol (trade name Actol ED-37B (number average molecular weight 3000); manufactured by Mitsui Takeda Chemical Co., Ltd.) was used as the polyol. As the isocyanate, methylene diphenyl diisocyanate (MDI) (trade name Millionate MTL-S; manufactured by Nippon Polyurethane) was used. As an amine-based catalyst, Kaolyzer No. 23NP was used. EP73660A manufactured by PANTECHNOLOGY was used as the organic acid salt catalyst. As the foam stabilizer, linear dimethylpolysiloxane (trade name: Niaxsilicone L5614; manufactured by GE Silicones) was used. The amount of each raw material used is as shown in Table 2.

A method for measuring the physical property values of the materials A to L will be described. Regarding the number of cells, the surface of the supply roller (3 locations in the axial direction × 8 locations in the circumferential direction) was observed with a scanning electron microscope (SEM), and the number of cells per inch was measured for each observed location, and the average value thereof. Was calculated. Regarding the aperture ratio of the cell wall, it was observed at a magnification of 100 to the outer peripheral surface by scanning electron microscopy (SEM) of the supply roller, the wall surfaces of the cells of the observed surface and the area S ₁ of the openings to calculate the total area S The aperture ratio (S ₁ / S × 100) was determined. Regarding the hardness, an aluminum disk having a diameter of 55 mm was pushed into the polyurethane foam layer, and the repulsive force in the indentation axial direction per unit length when the thickness of the polyurethane foam layer reached 70% was measured. This measured value (gf / mm) was taken as hardness. Regarding the density, the weight of the polyurethane foam layer was obtained by subtracting the weight of the core metal from the weight of the supply roller, the volume of the polyurethane foam layer was obtained based on the dimensions, and the density was calculated from the weight and the volume. The volume resistivity was obtained by normalizing a measured value obtained by applying 100 V with a high resistance meter R8340 manufactured by ADVANTEST, using a measurement probe based on JIS method K6911, with the thickness of the supply roller.

A plurality of experimental examples having different process conditions were set for each polyurethane foam material to be used. Specifically, Experimental Examples A1 to A5 using Material A, Experimental Examples B1 to B5 using Material B, Experimental Examples C1 to C5 using Material C, Experimental Examples D1 to D5 using Material D, Material Experimental Examples E1 to E5 using E, Experimental Examples F1 to F5 using Material F, Experimental Examples G1 to G5 using Material G, Experimental Examples H1 to H5 using Material H, Experimental Examples using Material I Experimental examples J1 to J5 using I1 to I5, material J, experimental examples K1 to K5 using material K, and experimental examples L1 to L5 using material L were set. In all the experimental examples, the rotation direction of the supply roller was set to a so-called width direction with respect to the developing roller. For each experiment, the ratio R of the peripheral velocity V _S of the supply roller to the circumferential speed V _D of the developing roller (V S _{/ V D),} the contact nip width between the supply roller and the developing roller, bite of the supply roller to the developing roller Amount, developing roller peripheral speed, first endothermic peak (glass transition point of internal material) and second endothermic peak (glass transition point of outer shell) measured by differential scanning calorimetry (DSC) The toner softening point was set as shown in Tables 3 and 4.

  Similar to Test 1, for each experimental example, 100,000 blank images were continuously printed using the above-described image forming apparatus, and a memory image confirmation image was printed every 10,000 sheets. In addition, evaluations regarding toner melting, fogging, memory image and developing roller contamination were performed in the same manner as in Test 1.

  The test results shown in Table 3 and Table 4 will be examined.

  In all the experimental examples, the toner did not melt and the evaluation of the fog was good. This is because the supply roller is set to rotate in the width direction with respect to the developing roller, so that the frictional force acting between the developing roller and the supply roller is reduced, and the heat generated in the nip portion of these rollers and toner This is thought to be due to the suppression of stress.

  Experiments A1 to A5 using Material A, Experiments B1 to B5 using Material B, Experiments C1 to C5 using Material C, Experiments D1 to D5 using Material D, Experiments using Material E For Examples E1 to E5, Experimental Examples F1 to F5 using Material F, Experimental Examples G1 to G5 using Material G, and Experimental Examples H1 to H5 using Material H, the contamination of the memory and the developing roller is evaluated. Both satisfy the acceptance criteria.

  On the other hand, experimental examples I1 to I5 using material I, experimental examples J1 to J5 using material J, experimental examples K1 to K5 using material K, and experimental examples L1 to L5 using material L In all cases, the evaluation of the contamination of the developing roller was bad, and the evaluation of the memory was bad except for Experimental Example J3.

  The reason why the contamination of the memory and the developing roller is poor in Experimental Examples I1 to I5 is that the number of cells of material I (27 cells / inch) is smaller than the number of cells of other materials (30 to 90 cells / inch). This is probably because the number of cells of the polyurethane foam layer in contact with the developing roller is small and the toner on the developing roller cannot be scraped off sufficiently by the supply roller. From this, it was found that the number of cells of the polyurethane foam layer is preferably 30 cells / inch or more.

  The reason for the poor evaluation of the developing roller contamination in the experimental examples J1 to J5 and the poor evaluation of the memory in the experimental examples J1, J2, J4, and J5 is that the number of cells of the material J (90 cells / inch) is a cell of another material. More than the number (27 to 80 / inch), too fine cells on the surface of the supply roller are filled with toner, and toner aggregates in the cells on the surface of the supply roller, so that the toner on the supply roller is scraped off. This is thought to be due to a decline in power. From this, it was found that the number of cells of the polyurethane foam layer is preferably 80 / inch or less. Accordingly, the number of cells in the polyurethane foam layer is preferably 30 cells / inch or more and 80 cells / inch or less. The reason why the evaluation of the memory was good in the experimental example J3 is that the peripheral speed ratio R (3.0) of the experimental example J3 is the peripheral speed ratio R (0.5) of the experimental examples J1, J2, J4, and J5. This is considered to be because the toner scraping power of the supply roller is increased.

  The reason for the poor evaluation of the contamination of the memory and the developing roller in Experimental Examples K1 to K5 is that the aperture ratio (58%) of the cell wall surface of the material K is higher than the aperture ratio (1 to 50%) of the cell wall surface of the other material. This is considered to be because the toner entering the inside of the polyurethane foam layer is gradually aggregated and the toner scraping power of the supply roller is reduced. From this, it was found that the opening ratio of the cell wall surface of the polyurethane foam layer is preferably 50% or less.

  The reason why the contamination of the memory and the developing roller is poor in the experimental examples L1 to L5 is that the opening ratio (1%) of the cell wall surface of the material L is higher than the opening ratio (3 to 58%) of the cell wall surface of the other material. This is considered to be because the material L has an almost complete closed cell structure. More specifically, when the polyurethane foam layer has a closed cell structure, it is difficult for the toner to enter the polyurethane foam layer, and the toner held on the supply roller is filled in cells near the surface of the polyurethane foam layer. . It is considered that the cells on the roller surface filled with the toner are difficult to scrape off the toner on the developing roller, and the toner collecting performance of the supply roller is lowered. From this, it was found that the opening ratio of the cell wall surface of the polyurethane foam layer is preferably 3% or more. Therefore, the opening ratio of the cell wall surface of the polyurethane foam layer is preferably 3% or more and 50% or less.

  In addition, Experimental Examples A1 to A5, B1 to B5, C1 to C5, D1 to D5, E1 to E5, F1 to F5, G1 to G5, and H1 to H5 that satisfy the acceptance criteria in all evaluation items are polyurethane foam layers The hardness is 1 gf / mm or 6 gf / mm. From this, it was confirmed that when the hardness of the polyurethane foam layer is 1 gf / mm or more and 6 gf / mm or less, an image can be formed satisfactorily by satisfying other conditions.

Furthermore, Experimental Examples A1 to A5, B1 to B5, C1 to C5, D1 to D5, E1 to E5, F1 to F5, G1 to G5, and H1 to H5 that satisfy the acceptance criteria in all evaluation items are polyurethane foam layers The density is 0.03 to 0.2 g / cm ³ . From this, it was confirmed that when the density of the polyurethane foam layer was 0.03 g / cm ³ or more and 0.2 g / cm ³ or less, an image could be satisfactorily formed by satisfying other conditions.

In addition, Experimental Examples A1 to A5, B1 to B5, C1 to C5, D1 to D5, E1 to E5, F1 to F5, G1 to G5, and H1 to H5 satisfying the acceptance criteria in all evaluation items are polyurethane foams The volume resistivity of the layer is 10 ² to 10 ⁶ Ωcm. From this, it was confirmed that when the volume resistivity of the polyurethane foam layer is 10 ² Ωcm or more and 10 ⁶ Ωcm or less, an image can be satisfactorily formed by satisfying other conditions.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present invention and a cross section of a developing device according to the present invention.

Explanation of symbols

1: Image forming apparatus, 12: Photoconductor, 16: Charging station, 18: Exposure station, 20: Development station, 22: Transfer station, 24: Cleaning station, 26: Charging apparatus, 28: Exposure apparatus, 30: Image light 32: passage, 34: developing device, 36: transfer device, 38: sheet, 40: cleaning device, 42: housing, 44: opening, 48: developing roller, 50: developing gap, 52: supply roller, 54: Core metal, 56: polyurethane foam layer, 66: contact portion (nip portion) between developing roller and supply roller, 68: toner.

Claims (4)

Development that makes the electrostatic latent image visible by attaching toner to the electrostatic latent image formed on the outer peripheral surface of the electrostatic latent image carrier and disposed opposite to the outer peripheral surface of the electrostatic latent image carrier. Laura,
A toner supply roller that is rotationally driven while being in contact with the outer peripheral surface of the developing roller, and that supplies and collects toner with the developing roller at the contact portion;
And the developing roller and the toner supply roller, a placed developing equipment to rotate so as to move in the same direction at their contact portion,
The toner supply roller has a cored bar and a polyurethane foam layer covering the outer peripheral surface of the cored bar,
The polyurethane foam layer has 30 to 80 cells per inch,
The opening ratio of the wall surface of the cell of the polyurethane foam layer is 3% or more and 50% or less ,
The polyurethane foam layer has a load per unit length received by the pressing surface of 1 gf / mm or more when pressed into a predetermined pressing surface to a depth of 30% of the thickness of the polyurethane foam layer. 6 gf / mm or less,
The density of the polyurethane foam layer is 0.03 g / cm ³ or more and 0.2 g / cm ³ or less,
The volume resistivity of the polyurethane foam layer is 10 ² Ωcm or more and 10 ⁶ Ωcm or less,
The amount of penetration of the polyurethane foam layer into the developing roller is 5% or more and 40% or less of the thickness of the polyurethane foam layer,
The contact nip width between the supply roller and the development roller in the circumferential direction of the supply roller is 3 mm or more and 6 mm or less,
The peripheral speed of the developing roller is 300 mm / s or more and 600 mm / s or less,
A regulating member for regulating the layer thickness of the toner on the developing roller is disposed in contact with or close to the outer peripheral surface of the developing roller at a position lower than a contact portion between the developing roller and the toner supply roller;
A toner having a capsule structure including an inner material and an outer shell covering the inner material;
The toner has an endothermic peak at the time of glass transition measured by differential scanning calorimetry (DSC) having a first peak of 10 to 30 ° C. and a second peak of 50 to 65 ° C. ,
A developing device , wherein the toner has a softening point of 70 ° C. or higher and 110 ° C. or lower as measured by a flow tester . 2. The developing device according to claim 1, wherein the developing device is produced by mixing a polyol, an isocyanate, a gas for forming bubbles, and a foaming agent that generates a gas by a chemical reaction with the isocyanate. The developing device according to claim 1, wherein a ratio of a peripheral speed of the toner supply roller to a peripheral speed of the developing roller is 0.5 or more and 3.0 or less. An image forming apparatus comprising the developing device according to claim 1 .

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