JP2000137379A - Roller comming into press-contact with latent image carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a roller comming into press-contact with a latent image carrier used in a developing device that can stably execute a soft press-contact development, and is reduced in cost and can form an image whose resolution is excellent and whose density fluctuation is reduced. SOLUTION: This roller is brought into press-contact with the latent image carrier 1 where an electrostatic latent image pattern is formed and formed of a foaming member 13 having a foam part 11 and a solid surface part 12, and the foam part 11 and the solid surface part 12 are constituted of the continuous phase of the same substance and a boundary does not substantially exist between them, and also the foaming member 13 has a density gradient in a thickness direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for forming an image by using an electrophotographic process,
The present invention relates to a roller that comes into pressure contact with a latent image carrier.

[0002]

2. Description of the Related Art A conventional developing device for performing development by pressing a toner carrier against a latent image carrier is disclosed in US Pat.
As disclosed in Japanese Patent No. 1146, a roller that uses a foamed member as a backing material (substrate), separately provides a soft conductive layer on the surface of the foamed member to form a toner carrier, and forms a toner carrier. There is known a developing device which transports toner to a developing device and performs development by pressing against a latent image carrier.

[0003]

However, in the conventional toner carrier as described above, in order to form a uniform conductive layer on the surface of the foamed member serving as the base material, the size of the cells of the foamed member is required. It is necessary at least to form the conductive layer so as to have the above film thickness, but it is not always easy to maintain and express the flexibility of the foamed member to the surface of the toner carrier. For this reason, there may be a problem that the development pressure and the development nip width (contact width) change due to environmental fluctuations and the like, which causes a density fluctuation and a decrease in resolution. In a toner carrier having a structure separated into two layers of a base material and a surface layer as described above, even in the manufacturing process, formation of a foamed member, machining of a foamed member, formation of a conductive layer, and the like are performed. A minimum of a series of steps is required, and since the foaming member is flexible, machining is particularly complicated and the processing time has to be long.
As a result, the cost of the developing device is increased.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and an object of the present invention is to stably perform soft pressure welding development using a flexible foam member. It is an object of the present invention to provide a roller which is used for a developing device which can be easily manufactured and which is inexpensive and which is in pressure contact with a latent image carrier.

[0005]

According to the present invention, there is provided a developing device comprising: a roller for pressing a latent image carrier having an electrostatic latent image pattern formed thereon, wherein the roller has a foam portion and a solid surface layer portion; The foam part and the solid surface layer part are made of a continuous phase of the same substance, and there is substantially no interface between them, and the foamed member has a density gradient in the thickness direction. It is characterized by the following.

[0006]

According to the above construction of the present invention, the roller is formed of a foamed member composed of a foam part and a solid surface part made of the same material, and the foam part and the solid surface part are made of a continuous phase of the same substance. Since there is substantially no interface between them and a density gradient is formed in the thickness direction of the foamed member, a roller having a particularly high-density solid surface layer can be formed. This allows
In addition to producing inexpensive pressure contact rollers that do not require complicated post-processing, soft pressure contact development utilizing the flexibility of the foam part and the flexibility of the solid surface layer is possible, and there is little damage to the toner and durability. It is possible to provide a highly reliable developing device.

With such a developing device, it is possible to provide a developing device having a simple structure, particularly using one-component non-magnetic toner.

Further, by forming the conductive layer on the solid surface layer portion, the developing electrode can be brought into closest contact with the latent image carrier to form a high resolution image with little edge effect. The present invention provides a developing device having a simple structure using a one-component non-magnetic toner, in which a conductive layer is provided on a toner carrier, so that toner can be held and transported by electrostatic image force when the toner is transported. Can be.

Further, by forming a magnetic field generating layer on the solid surface layer, the toner is restrained on the toner carrier by a magnetic force to stabilize the conveyance of the toner, and the background fog (non-image of the latent image carrier) Toner adhesion to a portion) can be prevented by magnetic force. Therefore, it is possible to provide a developing device having a simple structure, particularly using a one-component magnetic toner.

Further, since the toner carrier is roller-shaped and the solid surface layer is formed at least on the outer peripheral portion of the foamed member, the outer diameter is not polished, and the conductive layer and the magnetic field generating layer are formed on the solid surface layer. Thus, an outer diameter surface on which a functional layer such as the above can be easily formed is obtained.

Further, by forming the solid surface layer at the portion where the shaft is fixed to the shaft, the fixing strength between the shaft and the foamed member can be improved.

Further, by setting the thickness of the solid surface layer portion to 2 mm or less, it is possible to obtain sufficient flexibility for press-contact development.

Further, by forming the foamed member with a flexible foam, a sufficient pressure contact width can be obtained with a low developing pressure, and the fluctuation of the pressure contact state of the pressure contact portion can be reduced to stabilize the development density. In particular, when a foam material such as a polyurethane foam, a polystyrene foam, a polyethylene foam, an elastomer foam, and a rubber foam is used, a developing device having sufficient flexibility, being inexpensive, and excellent in mass productivity can be obtained.

[0014]

FIG. 1 is a schematic cross-sectional view of an image forming apparatus using a developing device in a specific embodiment to which the present invention is applied. The latent image carrier 1 is formed by forming a photosensitive layer 3 made of an organic or inorganic photoconductive material on a conductive support 2. After charging the photosensitive layer 3 using a charger 4 such as a corona charger or a charging roller,
The light emitted from a light source 5 such as a laser or an LED is formed into an imaging optical system 6.
The photosensitive layer 3 is selectively irradiated with light in accordance with an image through the process to obtain a potential contrast to form a desired electrostatic latent image pattern. On the other hand, the developing device 7 transports and develops the toner 8 which is an image forming body, and the toner carrier 9 which transports the toner 8 has a foam portion 11 formed of the same material on the outer periphery of a shaft 10 and a solid surface layer. Foamed member 1 having portion 12
3, a blade 14 made of a non-magnetic or magnetic metal or resin is pressed against the toner carrier 9 to charge the toner 8 to a predetermined polarity, and the toner layer is thinned to an appropriate amount. The toner 8 is held directly on the toner 9 and the toner carrier 9 is rotated to convey the thin toner 8. The toner carrier 9 is pressed against the latent image carrier 1 at a predetermined pressure, and the potential contrast of the latent image carrier 1 and the potential contrast of the latent image carrier 1 at or near this pressed portion.
A developing electric field is formed by a developing bias voltage applied between the toner carrier 9 and the latent image carrier 1 and the blade 14, and the charged toner 8 is developed according to the developing electric field. Thus, the electrostatic latent image pattern on the latent image carrier 1 is visualized by the charged toner 8. further,
The toner image is transferred onto the recording paper 16 by using a transfer device 15 such as a corona transfer device or a transfer roller, and the toner 8 is fixed to the recording paper 16 by using heat or pressure. 16 can be obtained.

FIG. 2 is a schematic cross-sectional view of an image forming apparatus using a developing device according to another embodiment of the present invention. Members having substantially the same functions and the same names as those in FIG. Is omitted. The developing device 20 transports and develops the non-magnetic toner 8, and forms a foam member 23 having a continuous foam portion 21 and a solid surface layer portion 22 with the same substance on the outer periphery of the shaft 10. The conductive layer 24 is formed on the solid surface layer portion 22, and the toner carrier 35 is configured by the shaft 10, the foam member 23, and the conductive layer 24. The toner carrier 25 is pressed against the latent image carrier 1 at a predetermined pressure, and the potential contrast of the latent image carrier 1 and the electric conduction between the latent image carrier 1 and the toner carrier 25 at or near the pressed portion. A developing electric field is formed by the developing bias voltage applied between the layer 24 or between the latent image carrier 1 and the blade 14, and the nonmagnetic toner 8 charged according to the developing electric field is developed. Thus, the electrostatic latent image pattern on the latent image carrier 1 can be visualized by the charged non-magnetic toner 8.

FIG. 3 is a schematic cross-sectional view of an image forming apparatus using a developing device according to still another embodiment of the present invention. Members having substantially the same functions and the same names as those in FIGS. The description is omitted here. The developing device 30 conveys and develops the magnetic toner 8, and forms a foam member 33 having a continuous foam portion 31 and a solid surface layer portion 32 of the same substance on the outer periphery of the shaft 10.
A magnetic field generating layer 34 is formed on the solid surface layer 32 of the above, and a toner carrier 35 is constituted by the shaft 10, the foam member 33 and the magnetic field generating layer 34. With the configuration in which the toner carrier 35 has the magnetic field generating layer 34, the magnetic toner 8 can be directly held on the toner carrier 35 by a magnetic force and conveyed by the leakage magnetic field on the surface of the magnetic field generating layer 34. The toner carrier 35 is pressed against the latent image carrier 1 at a predetermined pressure, and the potential contrast of the latent image carrier 1 and the potential contrast of the latent image carrier 1 at or near this pressed portion.
A developing electric field is formed by a developing bias voltage applied between the toner carrier 35 and the latent image carrier 1 and the blade 14, and the charged magnetic toner 8 is developed according to the developing electric field. . Thus, the electrostatic latent image pattern of the latent image carrier 1 is visualized by the charged magnetic toner 8.

In FIGS. 1 to 3, the photosensitive layer 3 of the latent image carrier 1 can be made of an organic or inorganic photosensitive material. The shaft 10 can be made of a metal material such as steel or aluminum, a resin material, or the like. Further, as the blade 14, a metal plate or a thin metal plate having a doctor knife shape at the tip, a resin or a resin film, or the like can be used.
In order to reduce the thickness of the toner layer on the toner carrier, it is preferable that the blade 14 is pressed against the toner carrier. Further, as the toner 8, widely known toners can be used irrespective of the presence or absence of magnetism, and both resin-based and wax-based toners can be used, and the configuration of the developer is not limited to one component.

Next, the foam member constituting the toner carrier will be described.

FIG. 4 is a diagram showing an example of the density distribution of the foam member of the developing device of the present invention. FIG. 4A is a diagram showing a density distribution of a foamed member in a specific example of the present invention.
The foam part has continuous foam cells and has sufficient flexibility, and in the vicinity of the outer periphery, the density distribution increases in the radial direction so as to draw a parabola, and the outer periphery is made of the same material as the foam part. A high-density solid surface layer having almost no foam cells (voids) is formed. Such a solid surface layer portion can be formed by a reaction injection molding method or the like in which a foaming material stock solution is injected and injected into a mold to react, and the thickness of the solid surface layer portion is 2 mm or less, preferably about several hundred μm. Thus, a toner carrier having a sufficient flexibility and a smooth surface can be formed without impairing the flexibility of the foam portion. As for the ratio of the thickness of the foam portion to the thickness of the solid surface portion, the ratio of the thickness of the solid surface portion to the thickness of the foam portion is in the range of 0.02 to 0.5, and more preferably 0.03 to 0.5. By setting the value in the range of 0.2, the pressure contact development can be further stabilized. When the above ratio is more than 0.5, the hardness of the surface layer increases and the flexibility becomes insufficient. On the other hand, when the above ratio is less than 0.02, pinholes are easily generated on the surface, which is not preferable.

FIG. 4B is a diagram showing the density distribution of the foamed member in another embodiment of the present invention. The foamed member is formed on the shaft by means such as vulcanization bonding or by integral molding with the shaft. The foam part has continuous foam cells and has sufficient flexibility, and the density increases substantially in a parabolic manner near the shaft part and the outer peripheral part, and at least the same material as the foam part at the outer peripheral part and the outer peripheral part of the shaft Thus, a solid surface layer having almost no foam cells (voids) is formed. Such a solid surface layer can be formed by a reaction injection molding method or the like in the same manner as in the example of FIG. 4 (a). By inserting this into a mold and integrally molding, it is possible to form a toner carrier having a small number of processing steps and high mechanical accuracy.

The foam portion can be used in any form of closed cell and open cell. However, closed cell is preferable because open cell has a large dimensional change due to temperature. Further, by setting the thickness of the foam portion to about 2 to 10 mm and the thickness of the solid surface layer to several hundred μm, the liner pressure becomes 1 to 5 g / mm, which is a very low pressure which was difficult with conventional rubber. The body can be pressed against the latent image carrier, and a stable pressure-contact state can be maintained to perform pressure-contact development without damaging the toner.
Further, as the foamed member, a flexible foam material is preferable, and a polyurethane foam, a polystyrene foam,
Polyethylene foam, elastomer foam, rubber foam and the like can be used. In particular, polyurethane foam is suitable for forming a conductive layer and a magnetic field generating layer on a solid surface layer portion because of its excellent moldability and high hydrophilicity. Furthermore, as a method for producing the foamed member, a gas mixing method, a foaming agent decomposition method, a solvent diffusion method, a chemical reaction method, a sintering method, an elution method, and the like can be used in addition to the reaction injection molding method. In any of the manufacturing methods, by forming the solid surface layer, a high-precision dimension can be obtained without post-processing, and a lightweight and low-cost toner carrier can be manufactured.

As shown in FIGS. 2 and 3, when a conductive layer or a magnetic layer is formed on the solid surface layer, a functional roller having high flexibility can be obtained. A specific example will be described below.

FIG. 5 (a) is a schematic cross-sectional view showing a specific example in which a conductive layer is formed on the surface of a toner carrier, and a foam portion 51 and a solid surface portion 52 are formed on a base 50 such as a shaft.
Are sequentially formed, and a conductive layer 53 is formed on the solid surface layer portion 52. By forming the conductive layer 53 on the outer peripheral portion of the toner carrier in this way, a developing bias voltage is applied to the conductive layer 53 via the thin toner layer at the time of press-contact development, so that the developing electrode is connected to the latent image carrier. A sufficient developing electrode effect is obtained by contact, and an edge effect (a state in which a strong electric field is generated at an edge portion of the image and excessive toner is developed) forms a high-resolution and excellent image having excellent area gradation. be able to.
As for the resistance of the conductive layer 53, if the resistance between the surface of the conductive layer 53 and the developing bias voltage applying section is 100 MΩ or less, a stable developing current can be obtained.
In order to ensure sufficient flexibility,
The thickness of the conductive layer 53 is preferably not more than 00 μm. When the conductive fine powder such as carbon black or metal is dispersed in the same resin as the foam part 51, the adhesion between the solid surface layer part 53 and the conductive layer 53 is reduced. Strength can be improved. As a method for forming the conductive layer 53, a uniform layer can be formed using spray coating, transfer coating, in-mold coating, roller coating, electroless plating, or the like.

FIG. 5B is a schematic cross-sectional view showing another specific example in which a conductive layer is formed on the surface of the toner carrier, and shows a solid surface layer 52, a foam portion 51, and a solid surface layer on a base 50 such as a shaft. The conductive layer 53 is formed on the solid surface layer part 52 by sequentially forming the parts 52. By forming the conductive layer 53 on the outer peripheral portion of the toner carrier as described above, a sufficient developing electrode effect can be obtained. Also, a solid surface layer 5 is provided at the joint between the shaft 50 and the foam 51.
By forming 2, the joint strength between the shaft 50 and the foam member can be improved, and the number of processing steps can be reduced by integrally molding the shaft 50 with the foam member. The solid surface layer 52 can be formed not only on the top and bottom of the foam part 51 but also on the edge of the foam part 51 and the like, so that toner is prevented from being mixed into the foam part 51. Can be.

FIG. 5 (c) is a schematic cross-sectional view showing still another specific example in which a conductive layer is formed on the surface of the toner carrier. The solid surface layer 52, the foam 51 and the solid surface 52 are formed on a base 50 such as a shaft. The surface layer 52 is formed in order, a conductive layer 53 is formed on the solid surface layer 52, and a protective layer 54 is formed on the conductive layer 53. Thus, the conductive layer 5
By forming the protective layer 54 on the surface 3, not only the durability of the conductive layer 53 can be improved, but also a charge control agent or the like can be mixed into the protective layer 54 to control the charge polarity and the charge amount of the toner. is there. The thickness of the protective layer 54 is preferably 100 μm or less, preferably about several μm, in order to ensure sufficient flexibility. In the case where a resin having excellent wear resistance such as a fluororesin is used and the charge of the toner is controlled, a dye or a pigment can be used.

FIG. 6A is a schematic cross-sectional view showing a specific example in which a magnetic field generating layer is formed on the surface of a toner carrier. A foam portion 61 and a solid surface layer portion 62 are sequentially formed on a base 60 such as a shaft. , A magnetic field generating layer 63 is formed on a solid surface layer portion 62. By forming the magnetic field generating layer 63 on the outer peripheral portion of the toner carrier as described above, the magnetic toner is held on the toner carrier by a magnetic force to stably convey the toner, and the scattering of the toner can be prevented. In addition, it is possible to reduce development fog by generating a development inhibiting force by a magnetic force against a developing force by a developing electric field. Further, the developing electrode effect can be obtained by making the magnetic field generating layer 63 conductive. The thickness of the magnetic field generating layer 63 is
In order to ensure sufficient flexibility, the thickness is preferably 100 μm or less. As for the material of the magnetic field generating layer 63, when the ferromagnetic fine powder is dispersed in substantially the same resin as the foam portion 61, the solid surface layer portion 62 is formed. The adhesion strength with the magnetic field generating layer 63 can be improved. As a method of forming the magnetic field generating layer 63, a uniform layer is formed using spray coating, transfer coating, in-mold coating, roll coating, electroless plating, or the like. can do. Here, as the ferromagnetic material used for the magnetic field generation layer 63, a material known as a magnetic recording material or a magnet material can be used. More specifically, Fe, Ni, C
a magnetic material containing at least one element of o, Mn, and Cr, for example, γ-Fe2O3, Ba-Fe,
Ni-Co, Co-Cr, Mn-Al or the like can be used, and the coercive force can be set to 200 Oe or more to prevent demagnetization of the magnetic field generating layer 63 due to magnetic toner and soft magnetic components around the developing device.

FIG. 6 (b) is a schematic cross-sectional view showing another specific example in which a magnetic field generating layer is formed on the surface of the toner carrier. The solid surface layer 62, the foam 61 and the solid surface layer 62 are formed on a base 60 such as a shaft. The surface portion 62 is formed in order, and the magnetic field generating layer 63 is formed on the solid surface portion 62. As described above, the magnetic field generating layer 63 is provided on the outer peripheral portion of the toner carrier.
By forming the magnetic toner, the magnetic toner can be stably conveyed on the toner carrier by the magnetic force, the scattering of the toner can be prevented, and the background fog can be reduced. In addition, a solid surface layer 62 is formed at the joint between the shaft 60 and the foam part 61 to improve the joint strength between the shaft 60 and the foam member, and the shaft 60 is integrally formed with the foam member to reduce the number of processing steps. Can be reduced. The solid surface layer 62 can be formed not only above and below the foam part 61 but also at the end of the foam part 61 and the like. With such a configuration, it is possible to prevent toner from being mixed into the foam portion 61.

FIG. 6C is a schematic cross-sectional view showing still another specific example in which a magnetic field generating layer is formed on the surface of the toner carrier. A solid surface layer 62, a foam 61 and a solid surface layer 62 are formed on a base 60 such as a shaft. Form the solid surface layer portion 62 in order,
A conductive layer 64 is formed on the solid surface layer 62 and the conductive layer 6 is formed.
4 on which a magnetic field generating layer 63 is formed. Thus, the conductive layer 64 and the magnetic field generating layer 6
By forming No. 3, a sufficient developing electrode effect can be obtained, and not only an image having high resolution and excellent area gradation can be formed, but also sufficient toner holding power can be obtained, and there is little ground fog and high contrast. An image can be formed.
The thickness of the conductive layer 64 is preferably set to 100 μm or less in order to secure sufficient flexibility.

FIG. 6D is a schematic cross-sectional view showing still another example in which a magnetic field generating layer is formed on the surface of the toner carrier, and shows a solid surface layer portion 62, a foam portion 61 and a solid portion 62 on a base 60 such as a shaft. Form the solid surface layer portion 62 in order,
The magnetic field generating layer 63 on the conductive layer 64 on the solid surface layer 62
And a protective layer 65 is formed on the magnetic field generating layer 63. By forming the protective layer 65 on the magnetic field generating layer 63 in this way, not only can the durability of the magnetic field generating layer 63 be improved, but also a charge control agent or the like can be mixed into the protective layer 65 to control the charge polarity of the toner. The charge amount can be controlled. still,
The thickness of the protective layer 54 is preferably 100 μm or less, and more preferably about several μm, in order to ensure sufficient flexibility. As for the material of the protective layer 54, a resin having excellent abrasion resistance, such as a fluororesin, can be used to improve the durability, and a dye or pigment can be used to control the charging of the toner.

Next, in the above-described example, a preferred example of a method for forming a toner carrier having a conductive layer on a solid surface layer will be further described.

First, a conductive hollow cylindrical member is prepared in advance, and a foamed member having a foam portion and a solid surface layer portion is formed therein to form a toner carrier. As the hollow cylindrical member in this case, a metal thin-walled cylindrical tube such as a Ni tube manufactured by an electroforming method, an Al tube or a Cu tube manufactured by an extrusion method, or the like can be used. . Next, a conductive resin tube is prepared in advance, and a toner carrier is formed in the same manner as described above. In this case, the resin tube may be anything that has flexibility and can be formed into a tube. For example, urethane, polyester, nylon, fluorine resin, polyethylene, polypropylene, vinyl chloride, silicone, acrylic rubber, chloroprene rubber, nitrile rubber, styrene butadiene rubber,
A material in which a conductive powder such as carbon black is dispersed in a material such as polybutadiene or polyisoprene can be used. Further, a material obtained by depositing or applying a conductive substance on the tube surface can also be used. Furthermore, in addition to the method of dispersing the conductive agent, the tube may be formed of a material using a conductive resin composition. Known methods such as an extrusion method and a die cutting method can be used as a method for producing the tube. Further, a heat-shrinkable tube made of these materials can also be used.

Further, as another method of forming the conductive layer, a metal of Al, Cr, or An may be directly deposited on the solid surface layer.

When the conductive layer is formed on the solid surface layer portion, depending on the material of the foaming agent, the exudation of the additive from the lower layer may cause contamination or damage of the photoreceptor or filming of the toner. In this case, an intermediate layer, that is, a bleeding prevention layer may be provided between the solid surface layer portion and the conductive layer.

Next, preferred characteristics of the roller according to the present invention will be described.

The surface of the toner carrier (roller) (the surface of the conductive layer and the protective layer, if present) has a roughness of 20 μm.
It is preferably Rz or less, more preferably 10 μm Rz or less.

In order to stably perform soft pressure contact development, the hardness of the roller is 10 to 70 based on Asuka C hardness.
Degree is preferable, and more preferably 20 to 35 degrees.

Further, since the roller made of a foamed member is an elastic body, if permanent deformation occurs in the roller, a change in the nip width between the photosensitive member and the toner carrier, a change in the pressing force applied to the photosensitive member, and the like will occur. This may cause significant image degradation. In order to reduce such defects, it is preferable that the permanent compression set (based on JIS-K-6301) of the roller is 20% or less.
% Or less, deformation due to pressure contact between parts can be substantially eliminated.

Next, the magnetic field generating layer will be described in more detail.

In a preferred embodiment of the present invention, the magnetic field generating layer comprises a heat-shrinkable sleeve in which magnetic powder is dispersed in a binder. As the binder in this case, polyurethane, polyvinyl chloride, polyethylene, polypropylene, linear polyester, polyamide resin, crystalline polyolefin, crosslinked polyolefin, non-crosslinked polyolefin, crystalline polyolefin copolymer, fluororesin, silicone rubber And a material having heat shrinkability such as EPDM. As the binder, in addition to polyurethane resin, vinyl copolymer such as vinyl chloride, fluorine resin, polyethylene, polypropylene, polyester, polyamide resin, polyolefin, epoxy resin, vinyl acetate, vinyl alcohol, vinyl butyral, vinyl formal, vinyl ethyl ester, etc. A system resin, nitrocellulose, cellulose acetobutyrate, or a mixture of these with another resin can be used. In addition, EPDM,
Any material having elasticity or flexibility, such as a rubber material such as fluorine rubber, silicon rubber, chloroprene rubber, natural rubber, isoprene rubber, butadiene rubber, neoprene rubber, and NBR, can be used as a binder.

As the magnetic powder to be dispersed in the binder, a known magnetic powder as a magnetic recording material or a magnet material can be appropriately used. Specifically, Fe, Ni, C
a magnetic material containing at least one element of o, Mn, and Cr, for example, γ-Fe2O3, BaO-6Fe
2O3, Co-γ-Fe2O3, Ba-Fe, Ni-C
o, Co-Cr, Mn-Al, etc. can be used.

In addition to the magnetic powder, a conductive powder such as a magnetic powder, a metal whisker, and carbon black can be contained. In this case, it is desirable that the carbon black has the ability to form a strong structure and acts so as to significantly reduce the electric resistance as the amount of carbon black added increases. Specifically, Ketjen black, acetylene black, lamp black, high-structure furnace black and the like can be used, and acetylene black having high conductivity is particularly preferable. Also, a smaller particle size is desirable for lowering the conductivity because a larger surface area per unit amount can be obtained.

Next, a method of manufacturing the above-mentioned sleeve type magnetic field generating layer will be described.

The sleeve type magnetic field generating layer can be formed by extrusion molding, injection molding, blow molding, vacuum molding, compression molding, transfer molding, centrifugal molding or the like. Among them, in particular, when the surface of the sleeve is to be mirror-finished, a centrifugal molding method in which molten resin is injected into the inner surface of a cylindrical mold that rotates at a high speed and molded is suitable. In addition, according to the extrusion molding method, a seamless sleeve having a constant film thickness can be continuously manufactured, so that the manufacturing cost can be reduced. Further, the surface roughness Rz of the extrusion die is set to 0.05 to 5
When the thickness is in the range of μm, a desired surface roughness can be imparted to the surface of the sleeve, so that surface treatment such as sandblasting can be omitted, and it is particularly desirable to manufacture an inexpensive developer carrier.

When forming the sleeve type magnetic field generating layer, it is advantageous to use a heat-shrinkable sleeve-coated roller. For example, after inserting the foamed member inside the sleeve before the heat shrinkage, the environment is decompressed, and further (120 ° C.
(2) The sleeve can be contracted by heating to cover the outer periphery of the foamed member to form a toner carrier. in this way,
By contracting the heat-shrinkable sleeve after decompression of the environment, the problem that air remains between the foamed member and the sleeve and a convex portion is formed on the sleeve surface is solved.

According to this method, since the heat-shrinkable sleeve is attached to the foamed member by the gripping force, it is not necessary to separately fix the heat-shrinkable sleeve and the foamed member with an adhesive. Further, even in the case of bonding the foamed member and the heat shrinkable sleeve, since the surface of the foamed member is covered with a relatively high-density solid surface layer, the adhesive impregnates the cells of the foam portion. Thus, the hardness of the foamed member is not excessively increased.

On the other hand, when the heat-shrinkable sleeve is directly coated on the outer periphery of the foam having a coarse cell, the heat-shrinkable sleeve shrinks by tracing the undulation of the cell in the foam portion. Only an agent carrier can be obtained.
On the other hand, in the method described above, if the heat-shrinkable sleeve is applied to the foamed member having the solid surface layer on the outer periphery of the foam, the solid surface layer can be made extremely smooth. There is also an effect that an agent carrier having an extremely smooth surface state can be obtained. still,
In the case where minute through holes are scattered in the solid surface layer portion, even if the step of decompressing the environment is omitted, no air pool is generated between the heat-shrinkable sleeve and the solid surface layer portion.

In this method, after the foam member is inserted into the heat-shrinkable sleeve, the one end of the heat-shrink sleeve is sequentially heated by a heating means such as an electric furnace or a drier to cover the outer periphery of the foam member. Is what you do. Also in this method, since the sleeve is sequentially covered with the foamed member from the end, a developer carrier having a smooth surface state can be obtained without generating air pockets.
Further, since the sleeve can be coated without depressurizing the environment, the coating device can be reduced in size,
It is particularly suitable for mass production because the coating time can be shortened.

In the above-mentioned heat shrinking method, for example, after the foamed member is inserted into the heat shrinkable sleeve, the foamed member is sequentially immersed in a hot water bath of, for example, about 90 ° C. from the end of the heat shrinkable sleeve to perform shrink coating. It is also possible to take a method.

The roller may be manufactured by shrinking a heat-shrinkable sleeve on the outer periphery of the foamed member and attaching the heat-shrinkable sleeve to the outer periphery of the foamed member, or by inserting a sleeve and shaft in which magnetic powder or conductive powder is dispersed into a mold. When integrally formed by a reaction injection molding method or the like, a roller with a small number of processing steps and high mechanical accuracy can be obtained.

Next, a method of magnetizing the roller will be described.

The method of magnetizing is not particularly limited.
It can be magnetized by in-plane magnetization or perpendicular magnetization.

In the in-plane magnetization method, the roller is rotated while the magnetic head is in contact with the magnetic field generating layer, and at the same time, the magnetization is performed while the magnetic head scans in the axial direction of the roller. This is a method of performing spiral magnetization at a minute pitch in the circumferential direction of the roller. In the roller according to the present invention, since the magnetic field generating layer is formed on a foamed member having elasticity, even when the magnetic head is in strong contact with the magnetic field generating layer, the flexibility of the magnetic field generating layer and the foaming are improved. The contact pressure of the head is dispersed and relieved by the elasticity of the member, so that the magnetic field generating layer can be prevented from being damaged as much as possible. Also, since the head gap portion and the magnetic field generating layer are in close contact, gap loss during magnetization is prevented. it can.

On the other hand, as the perpendicular magnetization method, for example, there is magnetic copying using a master magnet whose leakage magnetic flux density at the surface is 2000 gauss. As the master magnet in this case, a Nd-Fe-B-based rare earth magnet having a thickness of 1 mm and having a cylindrical shape can be used. In this magnet, a pitch of 1 mm is used so that the number of leaked magnets on the surface becomes 2000 Gauss. Is magnetized.

In the above-described example, the magnetic field generating layer is made of, for example, a 200 μm material in which γ-Fe 2 O 3 -based magnetic powder and carbon black are dispersed in a urethane-based binder.
It is obtained by providing on a foamed member with a thickness of m.
For the magnetization of the magnetic field generating layer, for example, while the magnetic field generating layer and the master magnet were in contact with each other so as to have a contact width of about 3 mm, both were rotated at the same peripheral speed to perform magnetic copying. Since the magnetic field generating layer is formed on the foam member, the roller is elastically deformed and comes into contact with the very hard master magnet without any gap, so that the magnet is uniformly magnetized at any position on the toner carrier. Was done.

In the case where the sleeve in which the magnetic powder is dispersed is used as the magnetic field generating layer, the sleeve can be preliminarily magnetized in the vertical direction, and then the foamed member can be covered or formed integrally.

As for the thickness of the magnetic field generating layer, according to the research results of the present inventors, it is clear that the larger the thickness of the magnetic coating film, the higher the magnetic restraining force can be obtained. More desirably, a good magnetic restraining force is obtained at 40 μm or more.

As for the coercive force of the magnetic field generating layer, a magnetic coating film having a larger coercive force can obtain a stronger magnetic constraining force. When the coercive force is 200 (Oe) or more, the magnetic constraining force is stable without attenuating. And maintain a coercive force of 2
By setting it to 000 (Oe) or more, a magnetic restraining force corresponding to a developing bias of about 100 V was obtained, and it was possible to prevent background fog due to the opposite polarity toner.

Further, since the toner is held and conveyed by the magnetic force, even if high-speed printing of 30 PPM or more is performed, no reduction in the density due to the insufficient toner supply is observed. Since a sufficient amount of toner can be supplied, the apparatus can be manufactured at a low cost in this respect as well, and the toner supply performance can be stabilized regardless of the amount of toner remaining in the hopper.

In order to exhibit the above-mentioned magnetic binding force, it is desirable that the toner contains 0 to 60% by weight, preferably 30% by weight or more of magnetic powder.

The thinner the magnetic powder dispersion sleeve constituting the magnetic field generating layer, the better the flexibility. According to the findings of the present inventor, it has been found that when the film thickness is 700 μm or less, flexibility that can be used for development is obtained, and in particular, when the film thickness is 300 μm or less, good flexibility is obtained.

The surface roughness (Rz) of the magnetic field generating layer is 0.1 to
5 μm is preferable, and the dynamic friction coefficient is preferably 0.2 to 0.7.

Next, the wear resistance of the magnetic field generating layer will be described.

FIG. 7A shows the change over time of the wear amount of the sleeve type magnetic field generating layer using an acrylic resin as a binder, and FIG. 7B shows the wear amount and the surface roughness of the sleeve surface. The relationship of Rz is shown. Since the surface of the sleeve is constantly rubbed via the toner particles at the position facing the elastic blade and the electrostatic latent image carrier, the surface wears over time as shown in FIG. As a result, as shown in FIG. 7 (b), the surface roughness Rz sharply decreases as the wear amount increases. In particular, the wear amount of the sleeve immediately after the start of use of the toner carrier is large. It was also observed that a large change in the amount of toner transport increased.

Therefore, if a sleeve having low abrasion resistance is used on the surface of the toner carrier, the surface of the sleeve is slid with toner even if a toner transport amount and a charge amount suitable for development are initially obtained. If the surface roughness and the coefficient of friction of the sleeve become unsuitable for toner conveyance or charging, the image will be formed with insufficient density. Further, when a flaw or the like occurs in the sleeve, the transport amount of the toner becomes non-uniform, resulting in an image having a lot of ground fog or an image with reduced fine line reproducibility.

As a result of further research based on the above findings,
The material of the sleeve covering the elastic layer is JIS-K731
1 In a wear test (wear wheel H22, 1000 rotation wear), when the wear amount is 700 mg or less, the sleeve surface is not easily worn away even when the developer is rubbed intensely, and it is used for a long time. As a result, it was found that a toner carrier having a constant surface roughness was obtained, and thus an image having sufficient image density and good resolution was stably obtained. Further, by setting the material of the sleeve to a wear amount of 200 mg or less in the above-described wear test, it is possible to reduce the initial wear of the sleeve significantly, and therefore, it is possible to reduce the long-term use from the start of use of the roller constituting the toner carrier. It has become possible to obtain an image with little fluctuation in density over the whole area.

As described above, by forming the magnetic field generating layer, the Asker C hardness of the roller increases by 2 degrees or more, preferably 5 degrees or more, and a layer having high hardness can be formed on the surface. By performing surface hardening in this hardness range, an effect of preventing stick-slip in the blade portion and the developing portion can be obtained.

In the present invention, a bleed-out preventing layer may be provided between the foam member and the magnetic field generating layer. This bleed-out prevention layer is for preventing bleed-out of the exudable substance, and is made of an oil-resistant layer made of resin or rubber. The resin or rubber constituting the oil-resistant layer has a solubility parameter (Solubility Parameter) SP and a foamed member. The solubility coefficient SPs of the plasticizer contained in the following formula: 2 ≦
Materials satisfying | SP-SPs | can be preferably used. Further, the magnetic field generating layer itself can be used as a bleed-out preventing layer.

According to the present invention, when the above-mentioned conductive layer or magnetic field generating layer is applied to the solid surface layer by the coating method, the paint does not substantially penetrate into the foamed member. It is possible to form such a conductive layer or a magnetic field generating layer having a high density. Further, even when the above-described conductive layer or magnetic field generating layer in the form of a tube is formed, the adhesion of these tubes can be made easier and stronger for the reasons described above, and the toner carrier having no unevenness on the surface. Can be formed.

[0069]

Hereinafter, the present invention will be specifically described with reference to more detailed examples. Example 1 A shaft and a foamed member of polyurethane foam were integrally formed by reaction injection molding using polyurethane as a main raw material.
A toner carrier having an outer diameter of 20 mm having a solid surface layer on the outer peripheral surface was formed. The surface of the toner carrier after molding can have any surface roughness depending on the surface condition of the mold,
By polishing the mold, a sufficiently smooth surface having a surface roughness of 5 μm or less was obtained, and post-processing such as outer diameter polishing of the toner carrier was unnecessary. The weight of the toner carrier excluding the shaft is 230 mm in length and 60 mm in outer diameter.
The weight was reduced to 5 g. When the toner carrier is pressed against a latent image carrier having an outer diameter of 60 mm at 2 g / mm, a developing nip width (contact width) of about 2 mm is obtained, and a developing device capable of maintaining a soft and stable pressure contact state. was gotten. When such a developing device is used in an image forming apparatus as shown in FIG. 1, 300 DPI line images, character images and solid images are continuously formed over 10,000 sheets, and the 300 DPI line images are stable without thickening. OD value 1.
4 or more high-density solid images could be stably formed. Further, no fixation or fusion state of the toner on the latent image carrier or the toner carrier was observed, and no damage to the toner was observed. However, the developing bias voltage was applied to the blade, and the image formation was performed in such a configuration that the toner carrier was neutralized after the development. Example 2 A shaft and a silicone rubber foam foam member were integrally formed by reaction injection molding using silicone rubber to which a conductive agent was added as a main raw material, and a conductive toner having an outer diameter of 20 mm having a solid surface layer on the outer peripheral surface was carried. Formed body. A sufficiently smooth surface was obtained on the surface of the toner carrier after molding, and post-processing such as outer diameter polishing of the toner carrier was unnecessary. Also,
The resistance between the surface of the toner carrier and the shaft provided a suitable conductivity of about several MΩ, and the development could be performed by applying a developing bias voltage to the shaft. When the toner carrier is pressed against a latent image carrier having an outer diameter of 60 mm at 2 g / mm, a developing nip width (contact width) of about 2 mm is obtained, and a developing device capable of maintaining a soft and stable pressure contact state. was gotten. When such a developing device is used in an image forming apparatus as shown in FIG. 1 and a line image, a character image and a solid image of 600 DPI are continuously formed over 10,000 sheets, the edge effect is small.
A DPI line image is formed stably without thickening, and a high-resolution image can be formed. The dot reproducibility is good, the area gradation is excellent, and the OD value is 1.4 or higher. A stable solid image could be formed stably.
Further, no fixation or fusion state of the toner on the latent image carrier or the toner carrier was observed, and no damage to the toner was observed. In addition, a toner carrier having an arbitrary resistance could be formed by using conductive fine particles such as carbon black as the conductive agent and changing the content of carbon black. Example 3 A shaft and a foamed member of polyurethane foam were integrally molded by reaction injection molding using polyurethane as a main raw material.
About 50μ of conductive paint with carbon black dispersed with polyurethane as binder on the surface of solid surface
m to form a conductive toner carrier having an outer diameter of 20 mm. A sufficiently smooth surface was obtained on the surface of the toner carrier after coating the conductive layer, and post-processing such as outer diameter polishing of the toner carrier was unnecessary. Also,
Even when this toner carrier was pressed against a latent image carrier having an outer diameter of 30 mm, sufficient flexibility and compression set characteristics were obtained. further,
The surface resistance of the toner carrier was 1 MΩ or less, and an appropriate conductivity was obtained, and development was performed by applying a developing bias voltage to the blade. When this toner carrier is pressed against a latent image carrier having an outer diameter of 30 mm at 3 g / mm, a developing nip width (contact width) of about 2 mm is obtained, and a developing device capable of maintaining a soft and stable pressure contact state. was gotten. When such a developing device is used in an image forming apparatus as shown in FIG. 2 and 600 DPI line images, character images and solid images are continuously formed over 1000 sheets, the edge effect is small and the 600 DPI line image is thickened. It is possible to form a high-resolution image stably without forming, excellent dot recording reproducibility, excellent area gradation,
A high-density solid image having an OD value of 1.4 or more could be formed stably. Further, no fixation or fusion state of the toner on the latent image carrier or the toner carrier was observed, and no damage to the toner was observed. Example 4 A shaft and a foamed member of polyurethane foam were integrally molded by reaction injection molding using polyurethane as a main raw material.
About 50μ of conductive paint with carbon black dispersed with polyurethane as binder on the surface of solid surface
m to form a protective layer by spray coating.
Further, a fluororesin was coated on the conductive layer to a thickness of about 1 μm to form a protective layer, thereby forming a conductive toner carrier having an outer diameter of 20 mm. A sufficiently smooth surface was obtained on the surface of the toner carrier after coating the conductive layer, and post-processing such as outer diameter polishing of the toner carrier was unnecessary. Even when the toner carrier was pressed against a latent image carrier having an outer diameter of 30 mm, sufficient flexibility and compression set characteristics were obtained. When this toner carrier was pressed against a latent image carrier having an outer diameter of 30 mm at 3 g / mm,
A developing nip width (contact width) of about 2 mm was obtained, and a developing device capable of maintaining a soft and stable pressure contact state was obtained. Using such an image forming apparatus as shown in FIG. 2, such a developing device was used to continuously form a 600 DPI line image, a character image and a solid image over 2000 sheets. A high-resolution image can be formed stably without forming an image, the dot recording reproducibility is excellent, the area gradation is excellent, and a high density solid image having an OD value of 1.4 or more can be stably formed. Could be formed. Further, no fixation or fusion state of the toner was observed on the latent image carrier or the toner carrier, no damage was observed on the toner, and the durability of the toner carrier was improved by the protective layer. . Example 5 A shaft and a foamed member of polyurethane foam were integrally molded by reaction injection molding using polyurethane as a main raw material.
A toner carrier having a conductive magnetic field generating layer having an outer diameter of 20 mm by applying a magnetic conductive paint in which γ-Fe2O3 and carbon black are dispersed with polyurethane as a binder on a surface of a solid surface layer to a thickness of about 10 μm. Was formed. A sufficiently smooth surface was obtained on the surface of the toner carrier after coating the magnetic field generating layer, and post-processing such as outer diameter polishing of the toner carrier was unnecessary. The toner carrier having the magnetic field generating layer is line-magnetized at a minute pitch with a magnetization reversal pitch of 50 μm, and a thin toner layer (toner film thickness of about 20 μm) of magnetic toner is held on the toner carrier surface by magnetic force. Was completed. Even when the toner carrier was pressed against a latent image carrier having an outer diameter of 30 mm, sufficient flexibility and compression set characteristics were obtained. Furthermore, the surface resistance of the toner carrier is 1 MΩ or less, and an appropriate conductivity is obtained.
The development could be performed by applying a development bias voltage to the shaft or the blade. When the toner carrier having the magnetic field generating layer magnetized at the fine pitch was pressed at 2 g / mm onto a latent image carrier having an outer diameter of 60 mm, a developing nip width (contact width) of about 2 mm was obtained. A developing device capable of maintaining a stable pressure contact state was obtained. Using such an image forming apparatus as shown in FIG.
When a line image of 00 DPI, a character image, and a solid image are continuously formed over 10,000 sheets, a line image of 600 DPI is formed stably without thickening with a small edge effect, and a high-resolution image can be formed. There was no tailing or background fogging at the edges of the image, the dot reproducibility was good, the area gradation was excellent, and a high-density solid image having an OD value of 1.4 or more could be formed stably.
In addition, there was no ground fog on the recording paper, and of course, there was no ground fog on the latent image carrier, so that the amount of waste toner could be greatly reduced, and reduction of ground fog due to the magnetic restraining force could be confirmed. Further, no fixation or fusion state of the toner on the latent image carrier or the toner carrier was observed, and no damage to the toner was observed. Example 6 By a reaction injection molding using polyurethane as a main raw material, a shaft and a foamed member of polyurethane foam were integrally molded,
A magnetic conductive paint in which γ-Fe2O3 and carbon black are dispersed using polyurethane as a binder is coated to a thickness of about 10 μm on the solid surface layer of the surface by roller coating to form a magnetic field generating layer, and a fluororesin is further formed on the magnetic field generating layer. Was coated to a thickness of about 1 μm to form a protective layer, and a toner carrier having a magnetic field generating layer with an outer diameter of 20 mm was formed. The surface of the toner carrier after coating the protective layer is
A sufficient smooth surface was obtained, and post-processing such as outer diameter polishing of the toner carrier was unnecessary. The toner carrier having the magnetic field generating layer was magnetized at a fine pitch, and a thin toner layer of magnetic toner could be held on the surface of the toner carrier by magnetic force. Further, 2 g of the toner carrier having the magnetic field generating layer magnetized at the fine pitch is placed on a latent image carrier having an outer diameter of 60 mm.
/ Mm, a developing nip width (contact width) of about 2 mm was obtained, and a developing device capable of maintaining a soft and stable pressure contact state was obtained. Using such an image forming apparatus as shown in FIG.
200 line images, character images and solid images
When formed continuously over 00 sheets, a line image of 600 DPI with a small edge effect is formed stably without thickening, and a high-resolution image can be formed. As a result, the dot reproducibility was excellent, the area gradation was excellent, and a high-density solid image having an OD value of 1.4 or more could be formed stably. In addition, there was no ground fog on the recording paper, and of course, there was no ground fog on the latent image carrier, so that the amount of waste toner could be greatly reduced, and reduction of ground fog due to the magnetic restraining force could be confirmed. Further, no fixation or fusion state of the toner on the latent image carrier or the toner carrier was observed, and no damage to the toner was observed. The durability of the toner carrier was improved by the protective layer. . Example 7 A shaft and a foamed member of silicone rubber foam were integrally formed by reaction injection molding using silicone rubber to which a conductive agent was added as a main material, and a solid surface layer was treated with a silane coupling agent to form an adhesive layer. Γ-Fe2O3 using polyolefin as a binder on the solid surface layer of the surface
The magnetic coating material dispersed with a thickness of about 10 μm is roller-coated to form a magnetic field generating layer, and the magnetic field generating layer is further coated with a fluororesin at a thickness of about 1 μm to form a protective layer. A toner carrier having a magnetic field generating layer of 20 mm was formed. A sufficiently smooth surface was obtained on the surface of the toner carrier after the coating of the protective layer, and post-processing such as outer diameter polishing of the toner carrier was unnecessary. Further, since the adhesive layer was provided at the interface between the solid surface layer and the magnetic field generating layer, the adhesion strength of the magnetic field generating layer to the solid surface layer could be improved. The toner carrier having the magnetic field generating layer was magnetized at a fine pitch, and a thin toner layer of magnetic toner could be held on the surface of the toner carrier by magnetic force. Also,
When the toner carrier having the magnetic field generating layer magnetized at the fine pitch was pressed at 2 g / mm onto a latent image carrier having an outer diameter of 60 mm, a developing nip width (contact width) of about 2 mm was obtained. A developing device capable of maintaining a stable pressure contact state was obtained. When such a developing device is continuously formed on 20,000 sheets of 600 DPI line image, character image and solid image using the image forming apparatus as shown in FIG. 3, the edge effect is small and the 600 DPI line image becomes thicker. A high-resolution image can be formed stably without the occurrence of tailing and background fogging at the edges of the image, the dot reproducibility is excellent, the area gradation is excellent, and the OD value is 1. 4 or more high-density solid images could be stably formed. In addition, there was no ground fog on the recording paper, and of course, there was no ground fog on the latent image carrier, so that the amount of waste toner could be greatly reduced, and reduction of ground fog due to the magnetic restraining force could be confirmed. Further, no fixation or fusion state of the toner on the latent image carrier or the toner carrier was observed, and no damage to the toner was observed. The durability of the toner carrier was improved by the protective layer. . Comparative Example 1 A shaft and a silicone rubber were integrally formed by injection molding using silicone rubber to which a conductive agent was added as a main raw material to form a conductive toner carrier having an outer diameter of 20 mm. After the molding, the surface of the toner carrier needs to be processed after the outer diameter polishing process of the toner carrier in order to remove unnecessary parts such as a parting line and obtain the outer diameter accuracy. The weight of the toner carrier excluding the shaft is 75 mm for a 230 mm length.
And could not be lighter. Even if this toner carrier is pressed against a latent image carrier having an outer diameter of 60 mm at 2 g / mm, almost no development nip width (contact width) is obtained, and even when a development nip width (contact width) of about 1 mm is obtained. , The toner carrier must be pressed against the latent image carrier with a pressing force of 20 g / mm or more, and the pressing mechanism parts and the like become large, and the latent image carrier, the toner carrier, and the toner may be damaged by pressure. Occurred. When such a developing device is used in an image forming apparatus as shown in FIG. 1, 600 DPI line images, character images, and solid images are continuously formed over 10,000 sheets. Only an image having a lot of images could be formed. In addition, it is difficult to form a normal image by causing scratches on the latent image carrier in the formation of about several tens of sheets and causing toner to adhere or fuse on the latent image carrier or the toner carrier. It was difficult.

Although the embodiments have been described above, the present invention is not limited to the above-described embodiments but can be widely applied to developing apparatuses such as electrophotography, and particularly, printers, copiers, facsimiles, and the like. Can be applied to displays.

[0071]

As described above, according to the present invention, soft pressure contact development can be stably performed using a flexible foam member, and an image with high resolution and little density fluctuation can be formed. Further, it is possible to provide a small-sized, light-weight and low-cost roller which is easy to manufacture and suitable for pressure contact development.

In particular, the roller is formed of a foam member having a continuous phase with the same substance and having a solid surface layer, and the solid surface layer is used as a toner carrying surface. Can be manufactured. Also,
Soft pressure contact development utilizing the flexibility of the foam portion and the flexibility of the solid surface layer portion is possible, and development with high durability with little damage to the toner can be realized.

Further, by forming the conductive layer on the solid surface layer portion, the developing electrode can be brought into closest contact with the latent image carrier to form a high resolution image with little edge effect.

Further, by forming the magnetic field generating layer on the solid surface layer, the toner is restrained on the toner carrier by the magnetic force, so that the conveyance of the toner is stable and the ground fog is prevented by the magnetic force. As a result, the amount of waste toner can be reduced.

Further, in the roller constituting the toner carrier, since the solid surface layer is formed at least on the outer peripheral portion of the foamed member, the outer diameter is not polished, and the conductive layer and the magnetic field generating layer are formed on the solid surface layer. Thus, an outer diameter surface on which a functional layer such as the above can be easily formed is obtained.

Further, by forming the solid surface layer at the portion where the shaft is fixed to the shaft, the fixing strength between the shaft and the foamed member can be improved.

Further, by setting the thickness of the solid surface layer portion to 2 mm or less, it is possible to obtain sufficient flexibility for press-contact development.

Furthermore, by forming the foamed member with a flexible foam, a sufficient pressure contact width can be obtained with a low developing pressure, and fluctuations in the pressure contact state of the pressure contact portion can be reduced to stabilize the development density.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an image forming apparatus using a developing device according to a specific embodiment to which the present invention is applied.

FIG. 2 is a schematic cross-sectional view of an image forming apparatus using a developing device according to another specific embodiment to which the present invention is applied.

FIG. 3 is a schematic cross-sectional view of an image forming apparatus using a developing device in still another specific embodiment to which the present invention is applied.

FIG. 4 is a diagram showing a density distribution of a foam member of the roller of the present invention.

FIG. 5 is a schematic cross-sectional view showing a specific example in which a conductive layer is formed on the roller surface of the present invention.

FIG. 6 is a schematic cross-sectional view showing a specific example in which a magnetic field generating layer is formed on the roller surface of the present invention.

FIG. 7 is a diagram showing mechanical characteristics of a magnetic field generation calendar formed on the roller of the present invention.

[Explanation of symbols]

 Reference Signs List 1 latent image carrier 7, 20, 30 developing device 8 toner 9, 25, 35 toner carrier 10 shaft 11, 21, 31, 51, 61 foam part 12, 22, 32, 52, 62 solid surface layer part 13, 23 , 33 Foamed member 50, 60 Base 24, 53, 64 Conductive layer 34, 63 Magnetic field generating layer

Claims (12)

[Claims] 1. A roller for pressing against a latent image carrier having an electrostatic latent image pattern formed thereon, the roller being formed of a foamed member having a foam portion and a solid surface layer portion, wherein the foam portion and the solid surface layer portion are formed. A foamed member having a density gradient in the thickness direction, comprising a continuous phase of the same substance and having substantially no interface between them, and being pressed against the latent image carrier. roller. 2. The roller according to claim 1, wherein a conductive layer is further formed on a surface of said solid surface layer portion. 3. The roller according to claim 1, wherein a magnetic field generating layer is further formed on a surface of said solid surface layer portion. 4. The roller according to claim 1, wherein said solid surface portion of said roller is formed at least on an outer peripheral portion of said foam member.
The roller according to 1. 5. The roller according to claim 4, wherein said foamed member is fixed around a shaft, and said solid surface layer is also formed at a fixed portion with said shaft. 6. The roller according to claim 1, wherein the thickness of the solid surface portion is 2 mm or less. 7. The foamed member is a polyurethane foam,
The roller according to claim 1, wherein the roller is formed by a flexible foam selected from the group consisting of polystyrene foam, polyethylene foam, elastomer foam and rubber foam. 8. The roller according to claim 1, wherein the hardness of the roller is in a range of 10 to 70 degrees (based on Asuka C hardness). 9. The roller according to claim 1, wherein the compression set of the foamed member is 20% or less (based on JIS-K-6301). 10. The roller according to claim 1, wherein a ratio of a thickness of the solid surface layer portion to a thickness of the foam portion is in a range of 0.02 to 0.5. 11. The density gradient curve of the cross section of the foamed member is S
The roller according to claim 1, wherein the roller is shaped. 12. The density gradient curve of the cross section of the foamed member is U
The roller according to claim 1, wherein the roller is shaped.