Patent Grant
9454103
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, printer, facsimile, or the like using an electrophotographic system.
2. Description of the Related Art
As a prior art relating to a hybrid development method (hereinafter, referred to as an HV development method), an image forming apparatus described in Japanese Patent Laid-Open No. H9-211970 is known. Japanese Patent Laid-Open No. H9-211970 discloses an image forming apparatus including a developing roller which carries a toner facing a photosensitive drum, and a conveying roller which carries a two-component developer including the toner and a magnetic carrier facing the developing roller. In the image forming apparatus, electric fields are made to act between the developing roller and the conveying roller to form a toner layer on a surface of the developing roller, and develop an electrostatic image of the photosensitive drum.
In the HV development method, since the charging of the toner is performed by stirring the two-component developer, a sufficient charging amount may be easily obtained, and since the supply of the toner from the conveying roller to the developing roller is performed by an electrostatic force, a toner charged to opposite-polarity is not supplied to the developing roller. Therefore, an occurrence of fog may be prevented by avoiding a toner adhesion to a non-image area of a photosensitive drum 1. Further, since only the toner is supplied to the developing roller, there are advantages such as adhesion of the magnetic carrier to the photosensitive drum 1 also being prevented or the like.
A potential difference ΔV is applied to the facing portion by a voltage applying portion 26. The toner of the developer in the facing portion is separated from the magnetic carrier on which the toner is electrostatically adhered by the ΔV, and projected in a direction of the toner carrying member 27 so as to be coated thereon. In this case, the ΔV and a charge amount Q/S in a unit area of the toner to be coated are in a proportional relationship as shown in Equation 1.
[Equation 1]
ΔV∝Q/S=M/S×Q/M (1)
Wherein, Q/S (μC/cm2) is a product of a toner amount M/S (g/cm2) in the unit area and the charge amount Q/M (μC/g) in a unit mass of the toner.
The toner coated on the toner carrying member 27 is conveyed to the facing portion with the photosensitive drum 1 to develop the electrostatic image on the photosensitive drum 1.
Meanwhile, in order to reduce energy consumption, a development device capable of outputting a high-quality image with a small toner amount is required. Therefore, speaking of the toner, by increasing an amount of pigment contained in the toner or improving dispersibility of the pigment, attempts to improve a density per toner have been made. However, in the HV development device, although the toner with improved density is used, it can be seen that an effect of suppressing the toner amount is limited.
As compared to a toner image (
A graph a of
Meanwhile, a graph b of
As described above, it is difficult to obtain a desired density with a small toner amount by using the HV development device and improve the density unevenness. Thereby, the present inventors examine the cause of a decrease in the density of the toner image developed on the photosensitive drum 1 in the HV development method. As a result, it can be seen that, in a method of coating the toner covered on the magnetic carrier by using the potential difference between both rollers as in the HV development device, the density of the toner image is easy to be reduced mainly by the following two reasons.
(1) When coating the toner on the surface of the toner carrying member 27 by the potential difference between the developer carrier 31 and the toner carrying member 27 illustrated in
(2) Further, when the toner carried on the toner carrying member 27 is projected to the photosensitive drum 1, in the case of the toner being formed in a multi-layered non-uniform toner layer as illustrated in
In consideration of the above-described circumstances, it is desirable to provide an image forming apparatus which obtains a high density image with a smaller toner amount.
An image forming apparatus includes:
a developing container which houses a developer having a non-magnetic toner and a magnetic carrier;
a concave-convex member which is rotatably disposed in the developing container, has a plurality of grooves formed in a rotation direction thereof, and is capable of carrying the developer;
a collecting portion which is disposed opposite the concave-convex member and collects the magnetic carrier carried on the concave-convex member; and
a receiving member which contacts the concave-convex member on a downstream side from the collecting portion in the rotation direction of the concave-convex member, and receives the toner carried on the concave-convex member,
wherein each groove formed in the concave-convex member has an inner surface configured to be in contact with the toner having an at least average particle diameter, and an apex having a smaller height than an apex of the toner in contact therewith, and each groove has side surfaces including a first side surface formed in one direction and a second side surface formed in the other direction in a circumferential direction of the concave-convex member, wherein the first side surface has a smaller inclination angle than the second side surface, and when a direction which moves down the first side surface in the circumferential direction of the concave-convex member is set to be positive, a relative velocity of a surface velocity of the concave-convex member to a surface velocity of the receiving member is set to be positive, at a position in which the concave-convex member and the receiving member come into contact with each other.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, development devices according to embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention describes an apparatus embodied as an image forming apparatus using an electrophotographic system as illustrated in
The photosensitive drum 1 is uniformly charged by a charging device 2, and then an information signal is exposed by, for example, a laser exposure device 3 to form an electrostatic image, and the formed electrostatic image is visualized by a development device 20. Next, a toner image on a surface of the photosensitive drum 1 is transferred to a transfer sheet 5 by a transfer charger 4, and further fixed thereto by a fixing device 6. Further, a transferred residual toner on the photosensitive drum 1 is cleaned by a cleaning device 7.
The concave-convex rotating member 22 as a concave-convex member is rotatably disposed in an opening 21A of the developing container 21 (inside of the developing container), and a plurality of convexes 22A having a predetermined height and a plurality of concaves 22B having a predetermined depth are formed on a surface thereof in a cross-sectional view as seen from a rotation axial direction thereof. The concave-convex rotating member 22 has a concave-convex structure in which the concaves 22B as a plurality of “grooves” is periodically formed in a rotation direction h. The concave-convex rotating member 22 is capable of carrying a toner 11 by the concaves 22B. The concave-convex rotating member 22 has a sleeve 221 rotatably supported in the developing container 21, and permanent magnets 222 which are non-rotatably supported inside of the sleeve 221 and have a plurality of magnetic poles.
The supply member 24 as a supply portion supplies the two-component developer 10 to the concave-convex rotating member 22. The supply member 24 is a screw for supplying the two-component developer 10 while stirring the same inside of the developing container 21.
The collecting roller 23 as a collecting portion is disposed opposite the concave-convex rotating member 22, and collects the two-component developer 10 (in particular, a magnetic carrier 12 carried on the concave-convex rotating member 22) which is not carried into the concaves 22B from the concave-convex rotating member 22. The collecting roller 23 has a sleeve 231 rotatably supported in the developing container 21, and permanent magnets 232 which are non-rotatably supported inside of the sleeve 231 and have a plurality of magnetic poles.
The photosensitive drum 1 as a “receiving member” is a member for carrying the electrostatic image. In addition, the photosensitive drum 1 contacts the concave-convex rotating member 22 on a downstream side from the collecting roller 23 in a rotation direction of the concave-convex rotating member 22, and receives the toner (the toner is transferred thereto) carried in the concaves 22B of the surface of the concave-convex rotating member 22. Additionally, the supply members 24, the collecting roller 23, and the photosensitive drum 1 are sequentially disposed at positions facing the surface of the concave-convex rotating member 22 from an upstream side in the rotation direction of the concave-convex rotating member 22.
Herein, the photosensitive drum 1 rotates in a rotation direction m, the concave-convex rotating member 22 rotates in a rotation direction h, and the collecting roller 23 rotates in an arrow i direction, respectively. A voltage from a voltage applying portion 26 is applied to the concave-convex rotating member 22 and the collecting roller 23.
The base layer 221a may be any material having conductive and rigid properties, and may be formed of SUS, iron, aluminum or the like.
The elastic layer 221b may include, as a base material, a rubber material having a suitable elasticity such as silicon rubber, acrylic rubber, nitrile rubber, urethane rubber, ethylene propylene rubber, isopropylene rubber, styrene-butadiene rubber or the like. The elastic layer 221b is a layer provided with conductive properties by adding conductive particles such as carbon, titanium oxide, metal fine particles or the like thereto. Besides the conductive fine particles, a spherical resin may be dispersed in the elastic layer 221b in order to control the surface roughness. In this example, the sleeve 221 includes the base layer 221a made of stainless steel, and the elastic layer 221b which is formed thereon and made of silicone rubber and urethane rubber with carbon dispersed therein.
The coating layer 221c is formed of a resin material. The convexes 22A are formed in the coating layer 221c. The plurality of convexes 22A is regularly arranged in the rotation direction h of the sleeve 221. Each of the convexes 22A are formed at an inclination pitch L, which is a dimension of the rotation direction h, and a height d.
Further, in order to increase adhesiveness of the coating layer 221c with the elastic layer 221b, a primer layer may be provided between both layers. In this example, the convexes 22A are formed in the coating layer on the elastic layer 221b, but the convexes 22A may be directly formed on the elastic layer 221b. In this regard, the coating layer may or may not be provided on the elastic layer.
In this example, the photosensitive drum 1 has the photosensitive layer on the roller-shaped base layer 221a, but a belt-shaped photosensitive belt may be used. In this regard, the elastic layer 221b may or may not be included in the sleeve 221. Specifically, the coating layer 221c made of a resin or metal may be provided on the base layer 221a and the convexes 22A may be formed in the coating layer 221c, or the convexes 22A may be directly formed on the base layer 221a.
Further, for preventing from being chipped or insulating processing, a high-hardness material and an insulating material may be coated on the coating layer having the convexes 22A, the elastic layer, or the base layer. In this case, it is necessary to form a thin coating layer enough to hold the convexes 22A thereon.
A direction which moves up the steep inclined surface SR with a steep inclination angle which is formed between the plurality of convexes 22A (between convexes) then moves down the gentle inclined surface SL with a gentle inclination angle (a direction which moves down the first side surface of the concave-convex member in the circumferential direction thereof) is set to be a positive direction in the direction along the plane of the sleeve 221. The convexes 22A are formed in a concave-convex structure arranged at the inclination pitch L from the steep inclination angle |κR| to the gentle inclination angle |κL| in the rotation direction h. In this regard, the groove formed in the concave-convex structure is arranged at pitch L of the grooves so as to contact the toner with the inner surface thereof. In other words, the case in which the toner cannot contact the inner surface of the groove is not included therein. That is, a concave-convex structure having a smaller pitch L of the grooves than the particle diameter of the toner is not included therein.
In this example, the inclination pitch L is 8 μm, a width xL of the gentle inclined surface SL is 7.3 μm, a depth d thereof is 1.9 μm, a maximum inclination κR of the steep inclined surface SR is 2.7, and a maximum inclination κL of the gentle inclined surface SL is 0.26. In addition, a thickness D of the coating layer 221c is 7 μm. Herein, the gentle inclined surface SL and the steep inclined surface SR are formed so as to extend parallel to the axis j (see
The present invention is not limited to the above-described structure, and any structure corresponding to a determination method of the concave-convex structure to be described below, may be included. Further, methods of forming and determining the concave-convex structure will be described in detail below.
The supply members 24 serve to stir the two-component developer 10 collected by the collecting roller 23 to be described below, convey to the supply portion W in which the concave-convex rotating member 22 and the supply members 24 face each other, and supply thereto by a magnetic force exerted by the permanent magnets 222.
Meanwhile, the sleeve 231 of the collecting roller 23 is rotatably provided so as to move in an opposite direction in a collecting portion U facing the concave-convex rotating member 22. A part of the two-component developer 10 supplied to the photosensitive drum 1 by the supply member 24 is collected by the magnetic force exerted by magnetic fields formed in cooperation with the permanent magnets 222 and permanent magnets 232, before being conveyed to the developing portion T. For this purpose, the collecting roller 23 may be disposed at a position upstream from the developing portion T and downstream from the supply portion W, in the rotation direction h of the concave-convex rotating member 22.
Next, coating the toner on the concave-convex rotating member 22 and developing the electrostatic image on the photosensitive drum 1 in the development device 20 will be described. A further detailed description will be described below. In the supply portion W, the two-component developer 10 is supplied by the supply members 24 to the concave-convex rotating member 22 having the concave-convex structure regularly arranged on the surface thereof.
During a conveying process of supplying the two-component developer 10 to the concave-convex rotating member 22 and collecting by the collecting roller 23, the toner of the two-component developer 10 in contact with the sleeve 221 of the concave-convex rotating member 22 contacts the concave-convex structure to be separated from the magnetic carrier, and is stably and uniformly coated thereon in a thin layer. The two-component developer 10 other than the coated toner is collected by the collecting roller 23 in the collecting portion U by a magnetic force, and stirred and again supplied to a path of an arrow k by the supply member 24, and then this process is repeated.
On the other hand, the toner which is not collected but is instead thinly and uniformly coated on the concave-convex rotating member 22 contacts the photosensitive drum 1 in the developing portion T, and is developed on the photosensitive drum 1 by the potential difference between the concave-convex rotating member 22 and the photosensitive drum 1. In this case, since coating of the concave-convex rotating member 22 is uniform in a regular manner, by properly setting a velocity ratio vh/vm determined by a moving velocity vh of the sleeve 221 and a moving velocity vm of the photosensitive drum 1, a uniform and high-density toner image may be developed on the photosensitive drum 1.
As an advantage compared to the HV development method which is a prior art, besides obtaining a uniform and high-density toner image, stability of the developing amount may be cited. For the HV development method, if the potential difference ΔV is determined, the coating amount depends on Q/M (following Equation 1).
[Equation 1]
ΔV∝Q/S=M/S×Q/M (1)
In other words, when the Q/M of the developer is varied due to environmental change or durability, the coating amount is varied, and the developing amount is largely varied according thereto. Therefore, in the HV development method, a complicated potential control by sensing the Q/M is required. In contrast, in the present invention, since the toner comes into multipoint contact with the inclined surface of the concave-convex structure formed on the concave-convex rotating member 22, it is possible to coat with a small electrostatic adhesion force as compared to the case of point contact with the plane. In other words, even when electrostatic adhesion force is varied due to the toner charge amount being varied, the toner amount coated on the concavo-convex structure is rarely varied, and therefore it is possible to achieve a stable coating amount, and achieve a stable developing amount without relying on a complicated control.
Hereinafter, coating the toner on the concave-convex rotating member 22 and developing the electrostatic image on the photosensitive drum 1 in the development device 20 will be described in detail. The two-component developer 10 in the developing container 21 is stirred and conveyed by the supply member 24 to the supply portion W. In this example, a positively charged toner is used having a number average particle diameter (D50) rt manufactured by a polymerization method of 7.6 μm, and an average circularity of 0.97. Because the toner is rotationally moved on the sleeve 221, the average circularity is preferably 0.95 or more.
As the magnetic carrier, a standard carrier P-01 (manufactured by the Imaging Society of Japan) having a number average particle diameter rc of 90 μm was used. Because a surface area capable of sufficiently contacting the toner to be coated and charging is required, the particle diameter rc of the magnetic carrier is preferably two times or more of the particle diameter rt of the toner. The number average particle diameter of the toner and magnetic carrier, and a method of measuring the average circularity of the toner will be described below.
The toner and magnetic carrier were mixed in a toner mass ratio (TD ratio x) of 7% to a total mass to prepare and use the two-component developer 10. In order to supply a sufficient toner amount to the sleeve 221, the TD ratio x is controlled so that a cover ratio S which is calculated as a rate of coating the magnetic carrier surface with the toner becomes 50% or more from the following Equation 2.
Wherein, ρc denotes a real carrier density (4.8 g/cm3), and ρt denotes a real toner density (1.05 g/cm3). The toner and the magnetic carrier are not limited, and any toner and magnetic carrier generally used and publicly known in the related art may be used. The two-component developer 10 conveyed to the supply portion W is supplied to the sleeve 221 by the magnetic fields produced by the plurality of permanent magnets 222 fixedly disposed inside of the concave-convex rotating member 22. The supplied two-component developer 10 is magnetically brushed under the influence of the rotation of the sleeve 221 and the magnetic fields produced by the permanent magnets 222, and conveyed in the rotation direction h of the sleeve 221.
While the two-component developer 10 is conveyed on the sleeve 221, among the toner coated to the magnetic carrier 12, the toner 11 in contact with the concave-convex structure comes into multipoint contact with the gentle inclined surface SL and the steep inclined surface SR. By this, the toner is bound on the concave-convex structure and separated from the magnetic carrier 12 to be coated on the concave-convex structure. In this case, since a binding force is applied only to the toner 11 in contact with the concave-convex structure, it is possible to uniformly coat the toner 11 in a thin layer on a regular structure.
Further, during the conveying process, the toner 11 adhered once on the sleeve 221 is also constantly in contact with the following conveyed magnetic carrier 12. When there is no concave-convex structure, since the toner adhered on the sleeve 221 has a smaller binding force than the concave-convex structure, the toner is easy to be collected in the magnetic carrier 12 in contact therewith. Therefore, scraping marks by the magnetic brush substantially parallel to the conveying direction of the two-component developer 10, herein, the rotation direction h of the sleeve 221, become significant, and it is not possible to uniformly coat the toner.
On the other hand, when the sleeve 221 has no concave-convex structure (see
The structure a of
Since the structure a is a concavo-convex structure having a large depth of the concaves 22B by increasing the height of the convexes 22A, the binding force is increased, and therefore an adhesion probability Q1 that the toner in contact with the surface of the sleeve 221 is separated from the magnetic carrier and adhered to the structure surface is high. Further, a scraping probability Q2 that the toner is scraped by the following conveyed magnetic brush is low. Therefore, coating to the concave-convex structure may be completed with a smaller supply amount. This effect can be seen from the graph a in
Since the structure b has a smaller depth of the concaves 22B by decreasing the height of the convexes 22A than the structure a, the adhesion probability Q1 is low, and the scraping probability Q2 is high. Therefore, compared to the structure a, the supply amount required to complete the coating is increased. This effect can be seen from the graph b in
On the other hand, since the structure c has a smaller binding force of the toner than the structures a and b, the adhesion probability Q1 is significantly low, and the scraping probability Q2 is significantly high. Therefore, even when increasing the supply amount, it is not possible to sufficiently coat the toner on the surface of the sleeve 221. This effect can be seen from the graph c in
By forming the concave-convex structure on the concave-convex rotating member 22, the toner 11 is arranged in the axis j to be periodically carried by the two-point contact in the concaves 22B in the rotation direction h in the cross-sectional view (see
In addition, efficiently transferring the toner 11 which is not scraped by the magnetic carrier 12 to the photosensitive drum 1 is related to a direction which moves up the steep inclined surface SR then moves down the gentle inclined surface SL, and a relative velocity of the concave-convex rotating member 22 to the photosensitive drum 1. This will be described with reference to
For example, in
On the other hand, for example, in
It is possible to consider that applying a torque to the toner 11 is the same as when coating the concave-convex structure, and by suppressing the toner 11 to be rotated in the arrow mt direction, the adhesion probability Q1 may be increased, and the scraping probability Q2 may be reduced.
In the state of
The carrier (circle c) has a predetermined particle diameter rc in contact with a first virtual line L1 connecting the apexes PL and PR (apexes with each other) of the convexes 22A formed on the surface of the concave-convex rotating member 22 and the toner 11. In this case, a force generating a torque for rotating the toner in the arrow mt direction about the apex PL does not act on the circle t.
On the other hand, if the particle diameter of the circle t exceeds the Rx, the second virtual line L2 is shifted from the apex PL of the inclined surface, the vertical component F⊥ acts as illustrated in
The Rx which is the maximum particle diameter of the toner 11 is geometrically calculated from the concave-convex structure (L=8 μm, xL=7.3 μm, d=1.9 μm, κR=2.7, and κL=0.26) used in this example, and the particle diameter of the magnetic carrier 12 (rc=90 μm) is 12 μm. Further, since the particle diameter rc of the magnetic carrier 12 is sufficiently larger than the inclination pitch L and the depth d, a contact point of the magnetic carrier 12 approximates the first virtual line L1.
A dotted line graph (a) is a particle size distribution of the toner 11 put into the developing container 21, and a solid line graph (b) is a particle size distribution of the toner 11 coated on the sleeve 221, after the developer is conveyed on the sleeve 221, and the two-component developer 10 is collected by the collecting portion of the developer to be described below. As illustrated in
On the other hand, in order to uniformly coat on the sleeve 221 in a thin layer, it may be not necessary to adhere a plurality of toners 11 on the steep inclined surface SR having the concave-convex structure. In order to prevent two or more toners 11 from being adhered, it is necessary that each toner 11 has a certain particle diameter or more with respect to the concave-convex structure. This will be considered using the following
As illustrated in
The Rn which is the minimum particle diameter of the toner geometrically calculated from the concave-convex structure (L=8 μm, xL=7.3 μm, d=1.9 μm, κR=2.7, and κL=0.26) used in this example is 1.7 μm.
From the above description, if the concave-convex structure and the particle diameter rc of the magnetic carrier 12 are determined, the particle diameter rt of the toner 11 that can be thinly and uniformly coated on the sleeve 221 has a relation of Rn≦particle diameter rt of the toner≦Rx, from the Rx and Rn geometrically calculated from
Herein, this example will be described again with reference to
The sleeve 231 is rotatably provided so as to move in the opposite direction in the collecting portion U facing the concave-convex rotating member 22. The concave-convex rotating member 22 and the collecting roller 23 are in non-contact with each other, and disposed at an interval of 2 mm or less. In this example, a voltage is applied to the collecting roller 23 by the voltage applying portion 26 so as to be equipotential with the concave-convex rotating member 22, but a float may instead be used.
The permanent magnets 222 in the concave-convex rotating member 22 have N and S poles disposed alternately two by two, respectively. Meanwhile, the permanent magnets 232 in the collecting roller 23 have two N poles and one S pole, respectively. Herein, as illustrated in
The size of the magnetic pole N22 and the magnetic pole S23 are set so that the width of the magnetic pole S23 is narrower than that of the magnetic pole N22, whereby the flux density of the magnetic field formed between the magnetic poles S23 and N22 changes so as to be increased from the concave-convex rotating member 22 toward the collecting roller 23 side. Therefore, the magnetic force acts on the magnetic carrier 12 from the concave-convex rotating member 22 to the collecting roller 23 in the collecting portion U, and the magnetic brush is formed along the magnetic field from the magnetic pole N22 to magnetic pole S23.
In addition, the sleeve 231 of the collecting roller 23 rotates in the rotation direction h of the sleeve 221 having the concave-convex structure, and in the arrow i direction of an opposite direction in the collecting portion U. Therefore, a conveying force directed inward of the developing container 21 from the collecting roller 23 is applied to the developer held by the magnetic force on the surface of the collecting roller 23, by the frictional force between the magnetic force thereof and the collecting roller 23 surface.
The developer carried on the surface of the collecting roller 23 is scraped by a scraper 25 whose one end is held by the developing container 21 in the vicinity of the position in which the N pole of the permanent magnet 232 is arranged, so as to be returned to the developing container 21. The developer returned to the developing container 21 is stirred with the newly replenished developer by the supply member 24, and again supplied to the concave-convex rotating member 22 in the supply portion W. That is, a circulation path in the developing container 21 for the two-component developer 10 containing the magnetic carrier 12 is illustrated by an arrow k in
Further, a potential difference is generated between the concave-convex rotating member 22 and the photosensitive drum 1 by the voltage applying portion 26, and the toner 11 provides a force in the direction of the photosensitive drum 1. In this example, the sleeve 221 and the photosensitive drum 1 are in contact with each other so that an entering depth therebetween is about 50 μm, and the moving velocity vh of the sleeve 221 is controlled so that a circumferential velocity ratio thereof becomes to be 1.05 times higher than the moving velocity vm of the photosensitive drum 1.
Further, with respect to the latent image potential (VL=100 V) of the photosensitive drum 1, a DC voltage of +400 V is applied to the concave-convex rotating member 22 by the voltage applying portion 26. By the circumferential velocity ratio, a torque acts on the toner 11 bound on the concave-convex structure to be rotated in the arrow nt direction, and due to the contact point between the sleeve 221 and the toner 11 being decreased, the binding force is reduced. Therefore, it is possible to reliably move the toner 11 bound on the sleeve 221 to the image portion Im (see
As illustrated in
Thereby, the adhesion force of the toner with the sleeve 221 is reduced, so as to be developed on the photosensitive drum 1. In this case, a condition for developing the toner on the photosensitive drum 1 in a high density is that the distance R between the centers of the toners 11a and 11b to be developed on the photosensitive drum 1 after t seconds is the rt or less.
The time t taken for the toner 11a to move the distance R is calculated by using the following Equation 3.
Since the toner 11b needs to move the distance of the inclination pitch L at time t, a relation shown in the following Equation 4 is obtained.
[Equation 4]
vht=L (4)
From Equations 3 and 4, the velocity ratio vh/vm of the sleeve 221 to the moving velocity vm of the photosensitive drum 1 has a relation shown in the following Equation 5.
In other words, in this example (rt=7.6 μm, and L=8 μm), the velocity ratio vh/vm required for developing the toner on the photosensitive drum 1 in a high density is 1.05 or more.
Table 1 shows results of a developing amount when varying the velocity ratio vh/vm, toner cover ratio on the photosensitive drum 1, and density evaluation after fixing in the development device 20. In addition, each evaluation method will be described below.
When the relative velocity of the moving velocity vh of the sleeve 221 to the moving velocity vm of the photosensitive drum 1 is negative (vh/vm=0.95, vm=300 mm/s, and vh=286 mm/s), it is not possible to develop the toner from the sleeve 221 to the photosensitive drum 1.
Meanwhile, the relative velocity of the moving velocity vh of the sleeve 221 to the moving velocity vm of the photosensitive drum 1 is positive, and the velocity ratio vh/vm satisfying Equation 5 is set to 1.05. In this case, it is possible to develop the toner 11 on the photosensitive drum 1 in a high density with a small toner amount, and achieve a desired density. Further, when developing the toner 11 in a multi-layer, the circumferential velocity ratio may be set by multiplying the circumferential velocity ratio (1.05) by the number of the desired toner layers.
Also, the relative velocity of the moving velocity vm of the photosensitive drum 1 and the moving velocity vh of the sleeve 221 will be further described. In
However, in
Table 2 shows the results of the developing amount when varying the velocity ratio vh/vm, toner cover ratio on the photosensitive drum 1, and density evaluation after fixing, by using toners having different particle diameters rt from each other.
If the velocity ratio vh/vm satisfying Equation 5 is set to 1.33, it is possible to develop the toner 11 on the photosensitive drum 1 in a high density with a small toner amount, and achieve a desired density. Further, when developing the toner 11 in a multi-layer, the circumferential velocity ratio may be set by multiplying the circumferential velocity ratio (1.33) by the number of the desired toner layers.
Furthermore, a relational equation of the velocity ratio vh/vm required for developing the toner in a high density is divided into the cases as described below, and is dependent on the inclination pitch L and the particle diameter rt of the toner. In addition, when setting the particle diameter rt of the toner, an inclination pitch L which is an interval between the convexes 22A, a distance R between the centers of the toners 11 carried on the surface of the photosensitive drum 1, and natural numbers n and m, and a relation thereof is set to n+1<(L/rt)≦n+2, and m−1<(rt/L)≦m, the velocity ratio vh/vm of the moving velocity vh of the surface of the concave-convex rotating member 22 and the moving velocity vm of the surface of the photosensitive drum 1 is derived from the following conditions.
Herein, the natural number n is determined by Equation 9.
[Equation 9]
n+1<(L/rt)≦n+2 (9)
Herein, the natural number m is determined by Equation 10.
[Equation 10]
m−1<(rt/L)≦m (10)
Tables 3 and 4 show results of the developing amount when developing the toner 11 on the photosensitive drum 1, the toner cover ratio on the photosensitive drum 1, the density evaluation after fixing, and image uniformity evaluation, which are obtained by the development device 20 of this example and the HV development device of the comparative example.
In the development device 20 according to this example, it is possible to develop a high density toner image on the photosensitive drum 1 with a small toner amount, whereas in the HV development device, even though the toner amount is controlled so as to be the same developing amount as the development device 20, the toner density is low, and a plurality of second-layered toner is present.
On the other hand, since the development device (see the graph (b) in
Table 5 shows results of developing amount when using the positively-charged toner obtained by varying the manufacturing conditions of the toner (polymerization and classification conditions) and the standard carrier P-01, toner cover ratio on the photosensitive drum 1, and the density evaluation after fixing, in the development device according to this example.
The desired images are obtained by toners A, B and D, whereas not obtained by the toners C and E. Since the toner C has an Rx which is the geometrically-calculated maximum particle diameter of the toner exceeding 12 μm, it is not possible to uniformly coat the toner on the sleeve 221. Therefore, the toner does not completely cover the surface of the photosensitive drum 1 resulting in only a partial exposure over a large region. When the toner is transferred onto the sheet, due to the influence of the white background portion over which the toner is not present, the image density is significantly reduced. In addition, image uniformity is deteriorated by the density unevenness.
Since the toner E has an Rn which is the geometrically-calculated minimum particle diameter of the toner being less than 1.7 μm, the toner is coated on the sleeve 221 in a multi-layer. In addition, the contact of the toner with the photosensitive drum 1 is reduced during developing, and a toner that cannot be developed occurs. Therefore, unevenness in the toner height on the photosensitive drum 1 occurs, and image uniformity is deteriorated.
According to the configuration of Example 1, it is possible to achieve the object of the present invention. In addition, the particle diameter rt of the toner may be within a range (Rn≦rt≦Rx) which is geometrically determined by the concave-convex structure and the particle diameter rc of the magnetic carrier. Further, for the non-magnetic toner, the particle diameter of 10% in the cumulative particle size distribution is Rn or more, and the particle diameter of 90% in the cumulative particle size distribution is Rx or less, preferably.
That is, the particle diameter of the toner is preferably Rn≦rt10≦rt90≦Rx. Thereby, it is possible to reduce negative effects that fine or coarse powders not developed on the photosensitive drum 1 are accumulated in the developing container 21, the charge stability is reduced or the like. Herein, rt10 is a particle diameter of 10% in the cumulative distribution, and rt90 is a particle diameter of 90% in the cumulative distribution.
The inclination pitch L of the concave-convex structure corresponds to the gap between the plurality of convexes 22A which are adjacent to each other in the rotation direction h, and may be less than three times the particle diameter rt of the toner, further preferably, is less than two times the particle diameter rt of the toner. Specifically, by limiting the inclination pitch L to two or less, further preferably, to one, variation in the coating amount between pitches may be suppressed, and the coating amount, and the stability of the developing amount may be improved.
Table 6 shows the evaluation results when varying the structural shape on the sleeve 221 in the development device according to this example. In addition, a maximum inclination angle |κL| of the gentle inclined surface SL of the convex 22A of the concave-convex structure is 0.5 or less, and a maximum inclination angle |κR| of the steep inclined surface SR of the convex 22A is 1.0 or more, preferably.
In structures A, B and C, only structure C was not achieved to the desired density. It is caused by that, while sufficient toner amount is coated on the sleeve 221 of structure C, the toner on the sleeve 221 is difficult to develop on the photosensitive drum 1. It is possible to consider that, in structure C, due to the maximum inclination |κL| of the gentle inclined surface SL being greater than 0.5, even though the toner on the sleeve 221 is provided with a prescribed circumferential velocity ratio, it is not possible to rotationally move on the gentle inclined surface SL, and it is difficult to develop on the photosensitive drum 1. From the above description, the maximum inclination |κL| of the gentle inclined surface SL of the concave-convex structure is preferably 0.5 or less.
Meanwhile, in structures D and E, only structure E did not reach the desired density. It is caused by that, the |κL| of structures D and E is 0.5 or less, respectively, and almost all the toner on the sleeve 221 can be developed on the photosensitive drum 1, but a sufficient toner amount is not coated on the sleeve 221 of structure E. It is possible to consider that the maximum inclination |κR| of the steep inclined surface SR is less than 1.0, and thereby, it is difficult to be bound on the sleeve 221.
From the above description, the maximum inclination |κR| of the steep inclined surface SR is preferably 1.0 or more. If the electrostatic adhesion force at the contact point between the toner 11 and the sleeve 221 is large, the toner is easy to be bound on the sleeve 221, and the stability of the coating amount is improved. Further, during the conveying process of the developer, it is not necessary to excessively increase the contact frequency and friction of the toner with the sleeve 221, and it is possible to suppress the deterioration of the developer.
For this purpose, an electrification series (electrification columns) of the surface of the sleeve 221 of the concave-convex rotating member 22, the magnetic carrier 12, and the non-magnetic toner 11 may be defined so that the magnetic carrier 12 is arranged between the toner 11 and the surface (coating layers 221c) of the sleeve 221 of the concave-convex rotating member 22. Under this condition, a difference in the electrification series between the surface material of the toner 11 and the sleeve 221 is greater than the difference in the electrification series between the toner 11 and the magnetic carrier 12.
Therefore, when the toner 11 and the sleeve 221 is in contact and frictionally charged, compared to the electrostatic adhesion force of the toner 11 and the magnetic carrier 12, a strong electrostatic adhesion force is generated, and the toner 11 is easy to be separated from the magnetic carrier 12 and then adhered to the sleeve 221. In addition, a method for determining the electrification series will be described below.
<Method of Forming a Concave-Convex Structure>
The concave-convex structure on the sleeve 221 may be formed by a photo nanoimprint process using a photo-curable resin, a thermal nanoimprint process using a thermoplastic resin, a laser edging process performing edging by scanning with a laser or the like. Alternately, the concave-convex structure on the sleeve 221 may be formed by a diamond edging process of mechanically grinding by a diamond blade, and further, replication by an electroforming technique from a molding thereof or the like.
As described above, in this case, the concave-convex structure may be directly formed in the elastic layer 221b in the sleeve 221, or may be formed in the coating layer 221c by previously applying the coating layer 221c made of a thermoplastic resin on the elastic layer 221b. In the photo nanoimprint process, the photo-curable resin is applied to the surface of the sleeve 221, and UV irradiated by a UV light source installed in place of the halogen heater, to form the concave-convex structure.
The sleeve 221 used in this example is formed by the photo nanoimprint process, and several nm of a primer layer is provided on the elastic layer 221b having a thickness of 2 mm in order to increase adhesion, and a fluorine photo-curable resin of several μm is applied thereon, to form the concave-convex structure.
<Method of Determining a Concave-Convex Structure>
Determination of the concave-convex structure on the sleeve 221 is performed by using an atomic force microscope (AFM) (Nano-I made by Pacific Nanotechnology Inc.) and measurement is performed according to the operation manual of the measuring device. The method of determining a concave-convex structure will be described below.
In this case, for a tip diameter rt of the probe, measurement is performed by sufficiently securing a resolution in the scanning direction. Specifically, it is preferably 1/10 or less of the tip diameter rt. The measuring method includes taking a difference in the obtained shape (position of the graph J2−position of the graph J1), further taking a derivation thereof, determining an apex P″, and determining bottom points YL″ and YR″ which are positioned on the left and right of the apex P″, respectively. When the convex 22A between the YL″ and YR″ is formed in a unit structure, maximum inclinations κL″ and κR″ of the gentle inclined surface SL″ (P″ YL″) and the steep inclined surface SR″ (P″ YR″), which are positioned on the left and right of the apex P″ of the convex 22A, respectively, are calculated.
Condition 1 . . . The maximum inclinations κLn″ and κRn″ of the gentle inclined surface SLn″ and the steep inclined surface SRn″ of the adjacent ten convex n structures (convex 1 to convex 10) of the convex n structures formed of the apex P″n and the left and right bottom points satisfy |κLn″|<|κRn″|. Further, it may be a condition that an average value of the maximum inclinations κLn″ and κRn″ of the gentle inclined surface SLn″ and the steep inclined surface SRn″ of the predetermined number (for example, ten) of convex n structures which are adjacent to each other in the rotation direction h satisfies Σ (|κLn″|/n)<Σ(|κRn″|/n).
Condition 2 . . . An L″n (L″1 to L″10) of a distance between the adjacent apexes satisfies Equation 11, and a ratio (xL″1/L″1 to xL″10/L″10) of a width xL″n of the gentle inclined surface SL″ to the L″n of the distance between the adjacent apexes satisfies Equation 12:
Herein, Equation 11 will be described. For example, a case of measuring the distance between the apexes by five points will be illustrated. Wherein, when being set as L″n1=7.8 μm, L″ n2=8.2 μm, L″n3=7.5 μm, L″ n4=8.5 μm, and L″n5=8.0 μm, a right side, since it is 10% of the average value of L″1 to L″5, becomes 0.8 μm. In a left side, for example, if subtracting the average value of L″1 to L″5 from L″1, the absolute value becomes 0.2 μm. For these reasons, an error in a particular pitch width of the distance between the apexes is within the error range of the average pitch width of the distance between the apexes.
In addition, when measuring the distance between the apexes by five points, when being set as L″n1=9.0 μm, L″n2=7.0 μm, L″n3=10.0 μm, L″n4=6.0 μm, and L″n5=8.0 μm, the right side, since it is 10% of the average value of L″1 to L″5, becomes 0.8 μm. In a left side, for example, if subtracting the average value of L″1 to L″5 from L″1, the absolute value becomes 1.0 μm. For these reasons, the error in the particular pitch width of the distance between the apexes is not within the error range of the average pitch width of the distance between the apexes.
For these reasons, the above-described Equation 11 or 12 mean that the error in the distance between the apexes, and an error in gentle inclined surface width to the distance between the apexes are within 10%. Thus, the concave-convex structure has the concaves 22B and the convexes 22A with a predetermined regularity in the rotation direction h, respectively.
A structure that satisfies the above conditions 1 and 2 is a concave-convex structure in which the convexes 22A having different inclination angles are regularly arranged, and it is determined to be a concave-convex structure according to the present invention. In addition, for a microstructure that the probe A cannot follow, a structure with a short pitch, and a structure with a long pitch that the probe B can enter, even though such structures are included, if there is the concave-convex structure according to the present invention, it is possible to obtain the effect of the present invention. Therefore, the sleeve 221 may include the above-described structure on the surface thereof.
<Method of Measuring a Concave-Convex Structure and Method of Defining a Particle Diameter of the Toner>
When the concave-convex structure is determined by the method of determining a concavo-convex structure, a method of measuring a concave-convex structure and method of defining a particle diameter of the toner will be described. For measuring, the sample used in the determination method is subject to measurement according to an operation manual of the measuring device using a non-contact surface and layer cross-sectional shape measurement system R5200 (manufactured by Ryoka Systems Inc.).
In
<Method of Measuring a Particle Diameter>
The particle diameter of the toner was measured using a Coulter Multisizer-III (Beckman Coulter, Inc.) according to the operation manual of the measuring device.
Specifically, 0.1 g of a surfactant as a dispersant was added to 100 ml of an electrolyte solution (ISOTON), and further, 5 mg of a measurement sample (toner) was added thereto. The electrolytic solution in which the sample is suspended was subjected to dispersion treatment with an ultrasonic disperser for about 2 minutes to use as a measurement sample. Using a 100 μm aperture, the number of the samples was measured for each channel, and a median diameter d50, 10% diameter d10 of the cumulative distribution, and 90% diameter d90 were calculated, and then the number average particle diameter rt of the sample was set to rt10 and rt90.
The particle diameter of the magnetic carrier was measured using a laser diffraction particle size distribution analyzer SALD-3000 (manufactured by Shimadzu Corporation) according to the operation manual of the measuring device. Specifically, 0.1 g of the magnetic carrier was introduced into the analyzer to perform a measurement, the number of samples was measured for each channel, and the median diameter d50 was calculated to determine the number average particle diameter rc of the sample.
<Method of Measuring Circularity>
A diameter, circularity and frequency distribution of the toner corresponding to the circle were measured using a FPIA-2100 type (manufactured by Sysmex Corporation), and calculated by using Equations 13 and 14.
[Equation 13]
Diameter corresponding to circle=(Particle projected area/π)1/2×2 (13)
[Equation 14]
Circularity=(Circumferential length of circle of the same area as particle projected image)/(Circumferential length of particle projected image) (14)
Herein, the “particle projected area” is an area of the binarized toner particle image, and the “circumferential length of particle projected image” is defined as a length of a contour line obtained by connecting edge points of the toner particle image.
The circularity in the present invention is an index illustrating the degree of concave-convexness of the toner particles, and is indicated as 1.00 when the toner particle has a completely spherical shape. As the surface shape is more complicated, the circularity becomes smaller. In addition, when the circularity (central value) at a division point i of particle size distribution is set to ci, and the frequency is set to fci, the average circularity C which means an average value of circularity frequency distribution is calculated from Equation 15.
[Equation 15]
Average Circularity C=Σi=1m(Ci×fci)/Σi=1m(fci) (15)
As a specific measuring method, 10 ml of ion-exchanged water from which solid impurities are previously removed was prepared in a container, and a surfactant as a dispersant, preferably alkylbenzene sulfonate was added thereto, and then 0.02 g of the measurement sample were further added, and evenly distributed. As a member for dispersing, an ultrasonic disperser Tetora 150 type (manufactured by Nikkaki Bios Co., Ltd.) was used, and the dispersion treatment was performed for 2 minutes, to use as a dispersion liquid for measuring. At that time, the dispersion liquid was appropriately cooled so that the temperature thereof did not increase to 40° C. or more.
For measuring a shape of the toner particles, a FPIA-2100 type was used, and the concentration of the dispersion liquid was controlled so that the toner particle density at the time of measurement was 3,000 to 10,000 particles/μl, such that more than 1000 particles were measured. After the measuring, the average circularity of the toner particles was calculated by using the measured data.
<Evaluation Method>
To determine the developing amount, the toner developed on the photosensitive drum 1 was sucked up, and the weight (mg) thereof and the area (cm2) of the suction portion were measured, and then, the weight (mg/cm2) of the unit area which is a division of them was calculated.
For the toner cover ratio, the surface of the photosensitive drum 1 on which the toner is developed is photographed by a microscope VHX-5000 (manufactured by Keyence Corporation), and required data was obtained from the image using image processing software Photoshop (manufactured by Adobe Systems Incorporated). Then, only an area of the toner unit (px) was extracted, and a ratio to a total area was calculated.
For density evaluation after fixing, developing, transferring, and fixing are sequentially performed to fix the toner image on a coated sheet, and evaluate the density thereof. For density evaluation, a reflection density Dr of the coated sheet was measured by a reflection densitometer 500 Series (manufactured by X-Rite Inc.), and with respect to a desired reflection density (CMY: Dr≧1.3, K: Dr≧1.5), the case of not achieving the desired reflection density is x, and the case of achieving the desired reflection density is ∘.
For evaluation of image uniformity of fixing degree, a halftone image (lightness L*≈70) wherein the density unevenness is easily-noticeable is subject to evaluation according to the following evaluation criteria.
Level good (∘): spotty density unevenness is hardly noticeable (0-3 points/cm2).
Level bad (x): spotty density unevenness is noticeably observed (4 points or more/cm2).
<Method of Determining Electrification Series>
Only the magnetic carrier is put in the developing container 21 of the development device 20, and a rotational operation in a normal development was performed for about 1 minute. In this case, an electric field applying portion is separated, and the concave-convex rotating member 22 and the collecting roller 23 were in a state of electrically floating.
A probe of a surface potential meter MODEL 347 (manufactured by Trek Inc.) is installed at a position of the developing portion T so as to face the concave-convex rotating member 22, and the surface potential of the concave-convex rotating member 22 was measured. The potential difference before and after the rotation operation (post-operation potential−potential before operation) was measured, and if the potential difference is plus or minus, it is possible to determine whether the sleeve 221 of the concave-convex rotating member 22 is positive side or negative side in terms of the electrification series, respectively, as compared to the magnetic carrier.
Meanwhile, by the triboelectric charging between the magnetic carrier and the toner, it is possible to determine whether the toner is either a positive side or negative side in terms of the electrification series as compared to the magnetic carrier, and thereby it is possible to determine the relative electrification series of three parties.
Tables 7 and 8 show the results of image evaluation performed by the development device 20 according to Example 1 under the following conditions 1 and 2. The sleeve 221 used in this example is formed by a thermal nanoimprint process. Several nm of a primer layer was deposited on the elastic layer 221b having a thickness of 2 mm in order to increase adhesion on the sleeve 221, and several μm of an amide thermoplastic resin was applied thereon, to form a concave-convex structure by the thermal nanoimprint process. The magnetic carrier was manufactured by controlling the particle diameter of a core by varying the sintering condition of a ferrite, and coating the ferrite core with a silicone resin. In addition, an HV development device using a developer used in conditions 1 and 2 was used in the comparative example.
<Condition 1>
Toner (negatively charged): rt=1.7 μm, and average circularity=0.96.
Magnetic carrier: rc=35 μm.
TD ratio: 4%.
Concave-convex structure (
Velocity ratio vh/vm=1.2.
<Condition 2>
Toner (negatively charged): rt=45 μm, and average circularity=0.95.
Magnetic carrier: rc=500 μm.
TD ratio: 7%.
Concave-convex structure (
Velocity ratio vh/vm=1.1
Regardless of the particle diameter and charge polarity of the toner, the effects of the present development device were confirmed. In other words, regardless of the particle diameter and charge polarity of the toner, since a high density toner image may be developed with a small toner amount, it is possible to obtain the desired density, and improve the density unevenness.
In this case, a width LFa of the flat portion M2 is smaller than three times the particle diameter rt of the toner, and is preferably smaller than two times thereof. Thereby, it is possible to coat a stable toner amount on the concave-convex structure. Of course, also in the structure, a relation between the maximum inclination κL and κR of the gentle inclined surface SL (PYL) and a steep inclined surface SR (PYR) which are positioned on the left and right of the apex P is |κL|<|κR|, as well as |κL| is 0.5 or less, and |κR| is 1.0 or more, preferably. Although not illustrated, the concave-convex structure may be a U-shaped inclination in which the gentle inclined surfaces SL and the steep inclined surfaces SR are continuously changed.
In this case, a width LFb of the flat portion M1 may be smaller than the particle diameter rt of the toner. Thereby, the toner to be coated on the flat portion M1 is limited, and it is possible to coat a stable toner amount on the concave-convex structure. Of course, also in the structure, a relation between the maximum inclination κL and κR of the gentle inclined surface SL (PYL) and a steep inclined surface SR (PYR) which are positioned on the left and right of the apex P is |κL|<|κR|, as well as |κL| is 0.5 or less, and |κR| is 1.0 or more, preferably.
It is preferable to set the aperture width Z to 1 μm or more and 100 μm or less.
The proportion of the flat portion M1 (at the convex portion) on the sleeve 221 is preferably set to 45% or less.
On the other hand, the toner amount required on the photosensitive member 1 is about the amount of toner with which toner particles are adhered to each other without any gap after fixing and a sheet can be covered with a toner image. Specifically, the total volume of the toner coated in the aperture portion St is more than the volume of the cube determined by the product of the toner layer thickness dt after fixing and the area Sa of the region S.
(Sta: the area (cm2) of the aperture portion St, Sa: the area (cm2) of the region S, ρ: toner true specific gravity (g/cm3), dt: toner layer thickness (cm) after fixing, κ: toner amount (g/cm2) at the aperture portion St)
The toner amount κ in the aperture portion St can be approximated by the following equation since the toner particles are substantially filled in the close-packed.
The toner layer thickness dt after fixing can be approximated by the following equation from the above two equations since it is possible to crush the toner particles to about ⅓ of the toner particle diameter rt, in the case of average condition.
In other words, when the proportion of the flat portion M1 on the sleeve 221 is 45% or less, it is possible to fix toner without any gap.
In case of the development device structures of Examples 1 and 2, when developing the toner image in a multi-layer on the photosensitive drum 1, the circumferential velocity ratio may be set by multiplying the values calculated under the conditions of Equations 6 to 8 by the number of desired toner layers. However, by increasing the circumferential velocity ratio, an image defect referred to as sweep-out may be generated.
The base layer may be any material having conductive and rigid properties, and may be formed of SUS, iron, aluminum or the like. The elastic layer includes, as a base material, a rubber material having a suitable elasticity such as silicone rubber, acrylic rubber, nitrile rubber, urethane rubber, ethylene-propylene rubber, isopropylene rubber, styrene-butadiene rubber or the like. The elastic layer is a layer provided with conductive properties in which conductive fine particles such as carbon, titanium oxide, or metal fine particles are added to a base material thereof.
Besides the conductive fine particles, a spherical resin may be dispersed in the elastic layer in order to control the surface roughness. In this example, the toner carrying member 27 including a base layer made of stainless steel, on which the elastic layer made of silicone rubber and urethane rubber with carbon dispersed therein is formed is used. The toner carrying member 27 is disposed so as to contact the photosensitive drum 1, and rotatably provided so as to move in the same direction at the developing portion T″ in the rotation direction of the photosensitive drum 1, as well as, is set so as to ensure both velocities are substantially equal to each other. Herein, the circumferential velocity ratio of both velocities is preferably 1 time or more but 1.1 times or less.
In this example, the toner carrying member 27 and the photosensitive drum 1 come in contact with each other, and for so-called contact developing, the toner carrying member 27 is made of a member having elastic or flexible properties, but, for non-contact developing, it is made of a material having conductive and rigid properties, and for example, may be formed of SUS, iron, aluminum or the like. The concave-convex rotating member 22 is disposed inside of the developing container 21 to face the toner carrying member 27 so as to come in contact therewith.
Therefore, at least one of the toner carrying member 27 and the concave-convex rotating member 22 needs to be made of a member having elasticity and flexibility. The concave-convex rotating member 22 includes a sleeve 221 which conveys the toner to the developing portion T″ facing the toner carrying member 27, and the plurality of permanent magnets 222 fixedly disposed therein. Further, the concave-convex structure according to the present invention is formed on the surface of the sleeve 221.
In this example, for the Ni—P layer of the sleeve 221 surface, the concave-convex structure is formed by the diamond edging process. The sleeve 221 is rotatably provided so as to move in the same direction as the toner carrying member 27 in the developing portion T″, and both velocities are set so as to have a circumferential velocity ratio determined by Equations 6 to 8, by the particle diameter rt of the toner and the concave-convex structure.
In this example, the particle diameter of the toner is 7.6 μm, and a particle diameter rc of the magnetic carrier is 90 μm. In addition, conditions of the concave-convex structure (
In this example, the toner carrying member 27 and the concave-convex rotating member 22 are rotated so as to move in the same direction, but they may move in the reverse direction. The collecting roller 23 is disposed opposite the concave-convex rotating member 22 and toner carrying member 27 with a gap, at a position upstream from the developing portion T and downstream from the supply portion W which supplies the developer to the concave-convex structure by the supply members 24 in the rotation direction of the sleeve 221.
The collecting roller 23 includes a sleeve 231 which collects the developer by the magnetic force and conveys the collected developer to the facing portion with the scraper 25 in the collecting portion U facing the concave-convex rotating member 22, and the plurality of permanent magnets 232 fixedly disposed inside thereof. Next, coating the toner on the toner carrying member 27 and developing the electrostatic image on the photosensitive drum 1 in the development device 20 which is a feature of the present invention will be described with reference to
The two-component developer 10 is supplied to the concave-convex rotating member 22 having the concave-convex structure on the surface thereof by the supply member 24. During a conveying process from supplying the two-component developer 10 to the sleeve 221 to collecting by the collecting roller 23 to be described below, the negatively charged toner of the two-component developer 10 in contact with the sleeve 221 is stably and uniformly coated thereon in a thin layer.
The two-component developer 10 other than the coated toner is collected by the collecting roller 23 in the collecting portion U by the magnetic force. On the other hand, the toner which is not collected but is instead thinly and uniformly coated on the concave-convex rotating member 22 contacts the toner carrying member 27 in the developing portion T, and is coated on the toner carrying member 27 by the potential difference generated by the voltage applying portion 26.
In this example, DC −400 V and DC −700 V voltages are applied to the concave-convex rotating member 22 by a voltage applying portion 26B and a voltage applying portion 26S, respectively. In this case, a direction which moves up the steep inclined surface then moves down the gentle inclined surface of the concave-convex structure is set to be positive, and the relative velocity of the moving velocity vh of the concave-convex rotating member 22 to the surface velocity vm of the toner carrying member 27 is positive. By properly setting the velocity ratio vh/vm of the concave-convex rotating member 22 to the toner carrying member 27, multi-layered and high-density toner coating on the toner carrying member 27 may be achieved.
Thereafter, the toner 11 carried on the toner carrying member 27 is conveyed to the developing portion T″ facing the photosensitive drum 1, and is developed under a condition in which the circumferential velocities of the photosensitive drum 1 and the toner carrying member 27 are substantially the same velocity. Therefore, it is possible to develop a high-density toner image with reduced sweep-out on the photosensitive drum 1.
Next, collecting of a residual toner 11″ remaining on the toner carrying member 27 without being developed will be described. The residual toner 11″ is conveyed to the collecting portion Y facing the collecting roller 23 by the toner carrying member 27. In this case, the toner 11″ contacts the two-component developer 10 carried on the collecting roller 23. Since the concave-convex rotating member 22 is coated with the toner in advance, the two-component developer 10 has a lowered TD ratio.
Therefore, since the developer has an ability for collecting the toner, and by contacting with the toner without being developed, the residual toner 11″ is separated from the toner carrying member 27, and is collected in the two-component developer 10 carried on the collecting roller 23. In this example, the collecting roller 23 is in an electrically floating state without applying a voltage thereto, but a voltage may be applied thereto.
In this case, in order to collect the residual toner 11″ in the collecting portion Y, the voltage applied to the collecting roller 23 is preferably a DC voltage VB or more (when using the positively charged toner, VB or less) applied to the toner carrying member 27. Meanwhile, when the voltage is applied to the collecting roller 23, the electric fields also act on the collecting portion U. Even under such a condition, the binding force of a component perpendicular to the direction of the electric field is generated in the toner coated on the sleeve 221 by the concave-convex structure.
Meanwhile, since the other developer is collected on the collecting roller 23, more stable and uniform thin-layer coating on the concave-convex rotating member 22 may be achieved. Further preferably, the magnetic poles (S23y pole) of the permanent magnets 232 disposed opposite the collecting portion Y and the magnetic poles (S23u pole) of the permanent magnets 232 disposed opposite the collecting portion U are the same polarity. A reason thereof will be described with reference to
Therefore, since the residual toner 11″ is easy to be collected by the magnetic carrier, it is possible to collect the residual toner 11″ with a lower electric field E73. Herein, it is not limited to the magnetic pole configuration, and the magnetic pole of the permanent magnet 232 disposed opposite the collecting portion Y and the magnetic pole of the permanent magnets 232 disposed opposite the collecting portion U may have the same poles as each other. In the collecting portions U and Y, the collected developer and the residual toner 11″ are returned to the developing container 21 by the magnetic field and the scraper 25, are agitated and conveyed by the supply member 24 again, and are supplied to the concave-convex rotating member 22 in the supply portion W.
The photosensitive drum 1 as a “toner carrying member” carries the toner. In addition, when a direction which moves up the steep inclined surface of the concave-convex structure then moves down the gentle inclined surface of the concave-convex structure is set to a positive, the relative velocity of the surface velocity of the concave-convex rotating member 22 to the surface velocity of the photosensitive drum 1 may be a positive.
In this example, the sleeve 221 includes, the base layer 221a made of stainless steel, the elastic layer 221b formed thereon in a thickness of about 3 mm and made of silicone rubber with carbon dispersed therein, and a coating layer 221c formed thereon in a thickness of about 7 μm. The concave-convex structure in the coating layer 221c is formed by curing a fluorine photo-curable resin by the photo nanoimprint process.
The developing container 21 has a supply member 24 for supplying the developer to the concave-convex rotating member 22, and a collecting member 23J for collecting the developer on the concave-convex rotating member 22, which are fixedly disposed inside thereof at intervals and face the concave-convex rotating member 22.
The supply member 24 conveys the two-component developer 10 collected by the collecting member 23J to be described below while stirring the same inside of the developing container 21 to the supply portion W in which the concave-convex rotating member 22 and the supply member 24 face each other, and the developer is supplied to the concave-convex rotating member 22 by the magnetic force exerted by the permanent magnets 222.
Meanwhile, the collecting member 23J as a “collecting portion” is formed of a magnetic material or a metal material having a higher magnetic permeability than a predetermined amount. The collecting member 23J collects the developer by the magnetic force exerted by the magnetic fields formed in cooperation with the permanent magnets 222. The collecting member 23J may be disposed at a position upstream from the developing portion T which moves the toner on the concave-convex structure to the photosensitive drum 1 and downstream from the supply portion W, in the rotation direction h of the sleeve 221. An anti-scattering sheet 28 for preventing the toner 11 from being scattered to an outside of the developing container 21 is provided in an opening of the developing container 21.
Herein, coating the toner on the concave-convex rotating member 22 and developing the electrostatic image on the photosensitive drum 1 in the development device 20 will be described. In the supply portion W, the developer supplied to the concave-convex rotating member 22 by the supply member 24 is conveyed in an arrow h direction in
Meanwhile, during the conveying process, since the toner which contacts the sleeve 221 to be coated thereon is not bound by the magnetic force, the toner passes through the collecting portion U and is conveyed to the developing portion T facing the photosensitive drum 1. A voltage is applied to the concave-convex rotating member 22 by the voltage applying portion 26, and a potential difference is generated between the concave-convex rotating member 22 and the photosensitive drum 1. In addition, the velocity ratio vh/vm of the moving velocity vh of the concave-convex rotating member 22 to the moving velocity vm of the photosensitive drum 1 is set so as to have a circumferential velocity ratio determined by Equations 6 to 8.
As described above, in the development device according to this example, it is also possible to stably develop a high-density image on the photosensitive drum 1 with a small toner amount, obtain a desired density, and improve the image uniformity. Further, since the development device according to the present invention includes the collecting portion having a simplified configuration, it is possible to adapt a decrease in size of the development device.
In this example, by using the belt 223, the concave-convex structure according to the present invention is directly formed on a base material thereof made of polyimide by the thermal nanoimprint process. Additionally, as another belt member, a coating layer formed of a thermosetting resin or photo-curable resin may be provided on the base material, and then a concave-convex structure may be formed on the coating layer by the nanoimprint process. In addition, a metal layer such as Ni—P having a low magnetic permeability may be provided on a base material of SUS by electroforming, and then a concave-convex structure may be formed on the metal layer by the diamond edging process.
Further, in order to prevent from being chipped or insulating processing, a high-hardness material and an insulating material may be coated on the concave-convex structure. In this case, it is necessary to form a thin coating layer enough to hold the concave-convex structure thereon. In this example, a power is fed to the elastic roller 225 disposed inside of the belt 223, but the power may be directly fed to the base material of the belt member. Instead of the elastic roller 225, the belt 223 may be provided with the elastic layer. In the development device according to this example, by using the belt 223, a conveying distance from the supply portion W to the collecting portion U may be changed, as necessary, and thereby, the limitation of an installation space may be prevented, as well as the conveying distance may be easily ensured.
In this example, by using the belt 223, the concave-convex structure is directly formed on a base material thereof made of polyimide by the thermal nanoimprint process. The collecting member 23J which is fixedly disposed on a position facing the permanent magnets 222 is preferably formed of a metal material such as iron having a higher magnetic permeability. In this example, the collecting member 23J is fixedly disposed, but it may be rotatably disposed such as a metal roller.
In the development device according to this example, by rotating the permanent magnets 222 disposed inside of the belt 223, the magnetic brush is conveyed while rotating on the belt 223. Therefore, it is possible to increase the contact frequency between the belt 223 and the toner by a short conveying distance and conveying time. In addition, by controlling the rotation velocity of the permanent magnets 222, variation in the coating amount may be suppressed without affecting other configurations.
The concave-convex structure in the coating layer 221c is formed by curing a fluorine photo-curable resin by the photo nanoimprint process. In this example, a supply and collecting member 29 plays a role of the supply member and the collecting member. The supply and collecting member 29 includes a sleeve 291 which is rotatably supported in the developing container 21, and permanent magnets 292 which are non-rotatably supported inside of the sleeve 291 and have a plurality of magnetic poles. The supply and collecting member 29 may be disposed so that the carried developer comes in contact with the concave-convex rotating member 22.
A process in which the toner is coated on the concave-convex rotating member 22 will be described. The developer supplied to the supply and collecting member 29 by a supply member 30 is conveyed in an arrow q direction in
Meanwhile, since the toner which contacts the sleeve 221 to be coated thereon is not bound by the magnetic force, the toner passes through the collecting portion U and is conveyed to the developing portion T facing the photosensitive drum 1. In this case, a potential difference is generated between the concave-convex rotating member 22 and the photosensitive drum 1 by the voltage applying portion 26. In addition, the velocity ratio vh/vm of the moving velocity vh of the concave-convex rotating member 22 to the moving velocity vm of the photosensitive drum 1 is set so as to have a circumferential velocity ratio determined by Equations 6 to 8.
In the developing portion T″, since the photosensitive drum 1 and the toner carrying member 27 rotate at substantially the same velocity, a high-density toner image with reduced sweep-out may be developed on the photosensitive drum 1. Herein, collecting of a residual toner remaining on the toner carrying member 27 will be described. Since the concave-convex rotating member 22 is coated with the developer collected by the supply and collecting member 29 in advance in the collecting portion U, the TD ratio is lowered.
Therefore, since the developer has an ability for collecting the toner, and by contacting with the residual toner without being developed, the residual toner may be collected. In this example, the supply and collecting member 29 is in an electrically floating state without applying a voltage thereto, but a voltage may be applied thereto. In this case, in order to collect the residual toner in the collecting portion Y, the voltage applied to the supply and collecting member 29 is preferably smaller than the DC voltage VB (when using the negatively charged toner, larger than the VB) applied to the toner carrying member 27.
Moreover, the magnetic pole of the permanent magnets 292 disposed opposite the collecting portion Y and the magnetic pole of the permanent magnets 292 disposed opposite the supply portion W have the same poles as each other, preferably. In addition, a configuration of collecting the residual toner by an independent collecting member may be used, as described in Example 3. In the development device according to this example, the supply and collecting member plays a role of the developer supply member and the collecting member. Therefore, there is no need to convey the developer between different members from each other, and it is difficult to generate a conveyance failure which can cause an immobile layer during conveying or the like. Accordingly, it is difficult to share the developer, and it is possible to improve the durability.
According to the configurations of Examples 1 to 7, during the supplying and conveying the two-component developer 10 on the plurality of convexes 22A of the surface of the concave-convex rotating member 22, the toner is uniformly coated thereon. In other words, the member carrying the non-magnetic toner may uniformly carry the non-magnetic toner of the developer. Further, after collecting the two-component developer 10 other than the uniformly coated toner, the toner between the plurality of convexes 22A moves to the receiving member.
In particular, when a direction which moves up the steep inclined surface SR with a steep inclination angle which is formed between the plurality of convexes 22A then moves down the gentle inclined surface SL with a gentle inclination angle is set to be positive, the relative velocity of the surface velocity of the concave-convex rotating member 22 to the surface velocity of the receiving member is set to the positive. Therefore, the toner carried between the plurality of convexes 22A reliably moves to the receiving member. In addition, a high density image is developed with a smaller toner amount from a monolayer to a multi-layer on the surface of the photosensitive drum 1.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This Application claims the benefit of Japanese Patent Application No. 2014-024651, filed Feb. 12, 2014, which is hereby incorporated by reference herein in its entirety.
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