JP2009020256A - Developing roller and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing roller having resin layers directly disposed on a conductive shaft, capable of stably forming images without causing an increase in residual potential on the surface thereof, on repeatedly forming images by using the developing roller. <P>SOLUTION: The developing roller has two resin layers formed around the conductive shaft. Provided that the surface resistance value of the layer constituting the surface of the developer roller is expressed by Rso and the surface resistance value of the layer adjacent to the conductive shaft is expressed by Rsu, the developing roller has a relation of 0.1≤Rsu/Rso≤10.0. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a developing roller used in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile receiver, and an image forming method using the developing roller.

  In an electrophotographic image forming method, a toner image is usually formed on a transfer sheet such as paper through the following procedure. First, an electrostatic latent image is developed by supplying a charged toner to an electrostatic latent image formed on an image carrier represented by an electrophotographic photosensitive member. Next, the toner image formed on the image carrier by development is transferred onto a transfer sheet. Further, the toner image on the transfer sheet is fixed by fixing, and a toner image is formed on the transfer sheet.

  Development methods for forming a toner image on an image carrier include a two-component development method using a two-component developer composed of a carrier and a toner, and a one-component development method using a one-component developer composed only of toner. . Among these, a developing method using non-magnetic one-component toner as one of the one-component developing methods forms a layer of toner frictionally charged on the developing roller surface by a charging member disposed near the developing roller or the developing roller itself, Toner is supplied to the image carrier by flying the layer-formed toner. In this way, image formation using non-magnetic one-component toner forms a toner image on the image carrier with a simple developing device, and is an effective means for realizing a compact full-color printer.

  Conventionally, the developing roller used in the non-magnetic one-component developing system has an elastic layer using silicone rubber or the like on the outer periphery of the conductive shaft, in order to ensure toner transportability and chargeability. Further, a surface layer was provided on the elastic layer. For example, there is a technique of using fluororubber for the surface layer from the viewpoints of improving the charging performance and toner transportability and preventing toner adhesion. Specifically, as a technique for forming a fluororubber layer on an elastic layer, a layer of a silane coupling agent is provided on the surface of the elastic layer, and a layer mainly composed of fluororubber or the like is formed on the elastic layer. There is a technique in which a surface layer is provided on a layer (for example, see Patent Document 1).

By the way, as represented by the appearance of home printers, recently, the spread of image forming apparatuses has been spurred, and along with this, the downsizing of apparatuses has been increasingly promoted. Against this background, the present inventor attempted to make the developing roller, which is a component of the developing device, compact, and studied a developing roller having a structure in which a resin layer was directly provided on the shaft. Then, for such a developing roller having no elastic layer, for example, the knowledge of a conductive roll technique in which a conductive resin layer is directly provided on a metal shaft (see, for example, Patent Documents 2 and 3). We investigated the improvement of the charging property of the roller. Furthermore, the functional separation of the resin layer was studied so that the adhesion of the resin layer to the shaft could be improved, and a developing roller having a two-layered resin layer was studied.
JP-A-8-190263 JP-A-5-257370 JP-A-5-297710

  However, when a developing roller having two resin layers formed on a conductive shaft was produced and image formation was attempted, when the image formation was repeated as in continuous printing, the developing roller charged a predetermined amount of toner. There was a tendency that it could not be applied. In other words, continuous image formation increases the potential on the surface of the developing roller and makes it difficult to charge the toner on the surface of the developing roller. As a result, fogging occurs due to toner scattering, and the image density is increased in high density portions and halftone portions. It became difficult to obtain. Further, in-machine contamination was caused by toner spillage of toner that was not sufficiently charged from the developing roller and the image carrier. This tendency was prominent when image formation was performed in a low temperature and low humidity environment.

  The present invention provides a developing roller capable of forming a stable image without causing an increase in potential on the roller surface when image formation is repeatedly performed using a developing roller having a resin layer directly provided on a conductive shaft. It is the purpose. In particular, an object of the present invention is to provide a developing roller that does not cause a potential increase on the surface of the developing roller even when continuous printing is performed in a low-temperature and low-humidity environment, and does not cause image defects or contamination inside the machine due to toner spillage.

  The present inventor has found that the above-described problem can be solved by any of the configurations described below.

The invention described in claim 1
“A developing roller having two resin layers around a conductive shaft,
Among the resin layers, when the surface resistance value of the layer constituting the developing roller surface is Rso and the surface resistance value of the layer adjacent to the conductive shaft is Rsu,
0.1 ≦ Rsu / Rso ≦ 10.0
A developing roller having the following relationship: ].

The invention described in claim 2
“Process for developing a latent electrostatic image on an image carrier by carrying the toner on the surface of a developing roller provided with two resin layers around the conductive shaft and supplying the carried toner onto the image carrier. An image forming method comprising:
The developing roller for supplying toner onto the image carrier;
Among the resin layers, when the surface resistance value of the layer constituting the developing roller surface is Rso and the surface resistance value of the layer adjacent to the conductive shaft is Rsu,
0.1 ≦ Rsu / Rso ≦ 10.0
An image forming method having the following relationship: ].

  In the present invention, a resin layer having a two-layer structure is provided on the conductive shaft, and by specifying the relationship between the surface resistance values Rs of the two resin layers, the potential increase on the surface of the developing roller can be achieved even when repeated image formation is performed. It became possible to suppress. As a result, even when continuous printing is performed, the potential is maintained at a level that does not cause image defects on the surface of the developing roller, and favorable image formation can be performed.

  In particular, in the present invention, even if continuous printing is performed in a low-temperature and low-humidity environment where residual charges are likely to occur and potential increases on the surface of the developing roller, the potential increase on the surface of the developing roller is suppressed. Occurrence of image defects due to charging defects and in-machine contamination due to toner spills have been resolved.

  The present invention relates to a developing roller having a structure in which a resin layer is directly provided around a conductive shaft. The developing roller is required to have good charge imparting performance on the roller surface and leak performance to move unnecessary charges from the resin layer toward the shaft. It has also been demanded to improve durability by firmly bonding the resin layer to the shaft surface. The present inventor has considered the two-layered resin layer as a means for simultaneously realizing these performances required for the developing roller.

  In the developing roller having a structure in which a resin layer is directly provided around the conductive shaft, since the resin layer is in direct contact with the conductive shaft, an unnecessary charge called a residual charge exists on the surface of the developing roller due to the structure. Also, it was considered that leakage was likely to occur toward the conductive shaft. Therefore, it has been considered that a developing roller having a two-layered resin layer is unlikely to cause a potential increase due to residual charges. However, with a developing roller having a two-layer resin layer, when the image formation is repeated, the potential on the roller surface increases, and the developing roller with the resin layer provided directly on the conductive shaft does not necessarily leak electric charges. Did not have.

  The present inventor considered that there is a factor that makes it difficult for the charge to leak from the conductive shaft when the resin layer has a two-layer structure, and speculated that the electrical resistance difference between the two resin layers hindered the movement of the charge. . That is, the interface between the two resin layers was considered to be a barrier that hinders the movement of charges. Therefore, the present inventor considered that if the electric resistance values of the two resin layers are aligned to a certain level, the barrier is eliminated and the charges can move smoothly between the layers. In this manner, in the developing roller in which the resin layer is directly provided on the conductive shaft, when the resin layer is divided into two layers, the surface resistance value of each layer is aligned to a certain level, thereby transferring the charge between the two resin layers. Found to promote.

  By the way, it is presumed that the idea of the present invention to promote the movement of charges between resin layers by aligning the surface resistance values of two resin layers to a certain level is not conceived from the technology of a developing roller having an elastic layer. Is done. The reason is that in the developing roller having an elastic layer, since the resistance value of the entire developing roller is governed by the resistance value of the elastic layer, there is a resistance difference between the two resin layers provided on the elastic layer surface. This is because it is estimated that the influence is canceled out by the resistance of the elastic layer. On the other hand, in the developing roller having a structure in which a resin layer is directly provided on the conductive shaft, the influence of the resistance difference between the two resin layers becomes obvious, and the resistance value of each layer constituting the resin layer is aligned to a certain level, It was necessary to create an environment where the charge transfer could be performed smoothly.

  Hereinafter, the present invention will be described in detail.

The developing roller according to the present invention has a resin layer composed of two layers around the conductive shaft, the surface resistance value of the upper layer constituting the surface of the developing roller is Rso, and the surface resistance value of the lower layer adjacent to the conductive shaft is When Rsu,
0.1 ≦ Rsu / Rso ≦ 10.0
It has the relationship.

  In the present invention, when the surface resistance value of the upper layer and the lower layer constituting the developing roller in which the resin layer is directly provided on the conductive shaft satisfies the above relational expression, the residual charge existing on the surface of the developing roller leaks from the conductive shaft. It has been found that an easy-to-operate state is formed. That is, even when the surface resistance value of the lower layer corresponding to the portion where the charge leaks to the conductive shaft is higher than the surface resistance value of the upper layer constituting the developing roller surface, the residual charge leaks toward the conductive shaft. It has been found that there are cases where it can be. It can be said that the effect of the present invention is expressed by forming an electrically barrier-free environment between the upper layer and the lower layer when the charge is moved from the upper layer to the lower layer. As described above, in the present invention, it has been found that the charging environment on the surface of the developing roller can be maintained by causing the residual charge formed on the surface of the developing roller to leak from the conductive shaft even in cases where the movement of charges is generally considered difficult. ing.

  If the value of the above relational expression is smaller than 0.1, the surface resistance value of the lower layer becomes too large compared to the upper layer, and it becomes difficult to move the charge from the surface of the developing roller toward the conductive shaft. The potential on the roller surface rises and a predetermined amount of charge cannot be applied to the toner. On the other hand, if the value of the above relational expression is larger than 10.0, the surface resistance value of the lower layer becomes too small and it becomes difficult to keep the charge on the surface of the developing roller, and a predetermined amount of charge is applied to the toner. Therefore, good image formation cannot be performed.

  In addition, the concrete numerical value of the surface resistance value of the upper layer and lower layer which comprises the said relational expression, its control method, and the measuring method of a surface resistance value are mentioned later. Here, of the two-layer resin layers constituting the developing roller, the layer constituting the surface of the developing roller is referred to as the upper layer, and the surface resistance value Rs is defined as Rso. A layer adjacent to the conductive shaft is called a lower layer, and its surface resistance value Rs is Rsu.

  FIG. 1 shows a typical sectional configuration of a developing roller according to the present invention. As shown in FIG. 1, the developing roller 10 has a resin layer 12 around the conductive shaft 11, and the resin layer 12 is formed on the conductive shaft 11 and an upper layer 12 a that is a resin layer constituting the surface of the developing roller 10. A two-layer structure composed of a lower layer 12b which is an adjacent resin layer is formed.

First, the conductive shaft 11 that holds the resin layer 12 is made of a conductive member. Specifically, a metal material such as stainless steel such as SUS304, iron, aluminum, nickel, an aluminum alloy, or a nickel alloy is preferable. . Also, a conductive resin in which a conductive material such as the above-described metal powder or carbon black is filled in the resin can be used. Conductive shaft 11, the specific resistance is preferably the following 1 × 10 ⁴ Ω · cm, also the outer diameter is preferably 5 mm to 30 mm, 10 mm to 20 mm is more preferable.

  Moreover, by making the resin layer 12 have a two-layer structure, a plurality of performances required for the resin layer 12 can be separated and expressed in the upper layer and the lower layer. That is, the resin layer 12 can be selected so that the resin for the upper layer 12a constituting the surface of the developing roller can positively charge the toner, and the resin for the lower layer 12b adjacent to the conductive shaft 11 can be charged. It is possible to select a resin that can actively leak.

  As a result, the upper layer 12a and the lower layer 12b exhibit different performances independently, and toner charging on the surface of the developing roller and charge leakage in the vicinity of the conductive shaft are less than those of the single layer developing roller. You will be able to do it efficiently. Further, by selecting a resin capable of expressing a strong adhesive force with respect to the conductive shaft 11 as the resin for the lower layer 12b, the resin layer 12 will not be peeled off from the conductive shaft 11, and the developing roller It is also possible to improve the durability.

  The total thickness of the resin layer 12 having a two-layer structure is preferably 1 μm or more and 200 μm or less, and more preferably 10 μm or more and 100 μm or less.

  The resin layer 12 (the uppermost layer 12a and the lower layer 12b) can contain a conductive material such as carbon black for the purpose of promoting the movement of electric charges. In this manner, the charge transfer in the resin layer 12 can be controlled by adding the conductive material to the resin layer, and the charge imparting performance of the toner on the surface of the developing roller can be controlled by the addition of the conductive material. That is, it is also possible to control the surface resistance values of the upper layer 12a and the lower layer 12b constituting the resin layer 12 by adding a conductive material.

As described above, in the present invention, when the surface resistance value Rso of the upper layer 12a and the surface resistance value of the lower layer 12b constituting the resin layer 12 of the developing roller 10 are Rsu,
0.1 ≦ Rsu / Rso ≦ 10.0
It has been found that when the above relationship is satisfied, a developing roller having a two-layer structure in which the effects of the present invention are exhibited can be obtained. In the present invention, when the surface resistance values of the upper layer 12a and the lower layer 12b satisfy the above relationship, the charge can be smoothly transferred between the upper layer 12a and the lower layer 12b, and the optimum amount for charging the toner on the surface of the developing roller. Therefore, smooth charging can be performed.

The specific value of the surface resistance value of the upper layer 12a and the lower layer 12b constituting the resin layer 12 is preferably 1.0 × 10 ⁶ Ω / □ or more and 1.0 × 10 ¹³ Ω / □ or less, and 1.0 × 10 6 ⁸ Ω / □ or more and 1.0 × 10 ¹¹ Ω / □ or less is more preferable. It is preferable that the ratio is within the range of the surface resistance value, and the ratio of the surface resistance values of both satisfies the above-described relational expression.

  The surface resistance value (Surface Resistivity, unit: Ω / □ (read as ohm-per-square)) indicates the electric resistance per unit area on the surface of the upper layer 12a and the lower layer 12b constituting the resin layer 12, and the sheet resistance or surface It is also called resistivity.

  The surface resistance value Rs of the upper layer 12a and the lower layer 12b is a value measured using the apparatus shown in FIG. FIG. 2 is a configuration diagram of a surface resistance measuring device 30 that measures the surface resistance value Rs of the developing roller. As shown in FIG. 2, the surface resistance measuring device 30 includes a developing roller 10, electrode rollers 31 </ b> A and 31 </ b> B, a DC power supply 32, and an ammeter 33.

The surface resistance value Rs is measured by the following procedure.
(1) First, both ends of the shaft 11 are pressed at 9.8 N so that the resin layer 12 (upper layer 12a, lower layer 12b) sufficiently contacts the electrode rollers 31A and 31B, and the developing roller 10 is rotated at 28 rpm.
(2) In this state, DC 100V is applied to the electrode roller 31A from the DC power source 32 for 5 seconds. A surface resistance value Rs is obtained by measuring the current value during application with the ammeter 33 and calculating the calculated current value and the voltage value. The measured value is an average value per unit application time (1 second).
(3) The measurement conditions by the surface resistance measuring device 30 are as follows. That is,
・ Measurement environment Temperature 23 ℃ ± 5 ℃, Humidity 57 ± 10% RH
Measurement is performed after the developing roller 10 is left in the above environment for 2 hours or longer. DC application time 5 seconds. Electrode roller diameter 12 mm.
A specific example of the surface resistance measuring device 30 in FIG. 2 is, for example, an electric resistance meter “HIOKI 8806 type (manufactured by Hioki Electric Co., Ltd.)”.

  Specific methods for controlling the surface resistance value Rs (the surface resistance value Rso of the upper layer 12a and the surface resistance value Rsu of the lower layer 12b) of the resin layer 12 (upper layer 12a, lower layer 12b) include the following methods. That is, there is a method of adjusting the surface resistance values of the upper layer 12a and the lower layer 12b by adding a conductive material typified by carbon black into the resin layer 12 and controlling the amount of addition. That is, if the amount of the conductive material added to the resin layer 12 is increased, the conductivity of the resin layer 12 is increased and the surface resistance value is reduced. On the other hand, if the addition amount of the conductive material decreases, the conductivity of the resin layer 12 decreases and the surface resistance value increases.

  There is also a method of controlling the surface resistance value by adjusting the thickness of the resin layer 12. That is, increasing the thickness of the resin layer decreases the conductivity of the resin layer and increases the surface resistance, while decreasing the thickness of the resin layer increases the conductivity of the resin layer and decreases the surface resistance. Furthermore, there is a method of controlling the surface resistance value based on the conductivity of the conductive material. For example, a material having a high electrical conductivity (low resistance) is selected and the conductivity of the resin layer is increased to increase the surface resistance value. On the other hand, the surface resistance value is increased by selecting one having low electrical conductivity.

  Examples of the conductive material that can be used in the present invention include, in addition to carbon black and graphite, various conductive metals or alloys such as aluminum, copper, tin, and stainless steel, zinc oxide, titanium oxide, tin oxide, indium oxide, Examples thereof include metal oxides such as tin oxide-antimony oxide solid solution and tin oxide-indium oxide solid solution, and fine powders such as insulating substances coated with these conductive materials. Among these conductive materials, carbon black is preferable because it is relatively easily available and can exhibit good chargeability. Carbon black, which is a representative example of the conductive material, will be described in detail later.

  These conductive materials preferably have an average particle size of 5 nm to 100 nm. Moreover, 5-70 mass parts is preferable with respect to 100 mass parts of resin, and, as for the addition amount in the resin layer 12, 20-50 mass parts is more preferable. Moreover, the titanium oxide mentioned above can use what has crystal forms, such as anatase type, a rutile type, a brookite type, and an amorphous structure.

  Next, carbon black which is one of conductive materials that can be added to the resin layer 12 will be described. The type of carbon black that can be added to the resin layer 12 is not particularly limited. Specific examples of carbon black include furnace black, gas black, channel black, frame black, thermal black, acetylene black, and plasma black. Inversion blacks disclosed in DE19521565, silicon-containing carbon blacks disclosed in WO98 / 45361 and DE19631396, metal-containing carbon blacks disclosed in WO98 / 42778, arc discharge blacks (Lichbogenruss), And carbon black etc. which are obtained as a by-product by a chemical manufacturing method are mentioned. In addition, carbon black added as a reinforcing filler to rubber mixtures, carbon black used for stabilizing UV rays, carbon black used as a reinforcing filler in applications other than rubber such as bitumen, and plastics Examples thereof include carbon black added as a filler and carbon black used as a reducing agent in metallurgy.

  As described above, the carbon black content in the resin layer 12 is preferably 5 to 70 parts by mass and more preferably 20 to 50 parts by mass with respect to 100 parts by mass of the resin. By setting the carbon black in the above range, the movement of electric charges in the resin layer 12 is appropriately controlled. That is, since charge leakage from the resin layer 12 toward the conductive shaft 11 can be appropriately performed, unnecessary charge does not remain on the surface of the developing roller, and the surface potential of the developing roller can be maintained at a predetermined level. it can. Accordingly, proper toner charging can always be performed on the surface of the developing roller, and a predetermined amount of toner can fly and be supplied from the surface of the developing roller to the image carrier, so that proper image formation can be stably performed.

  In addition to the above-described carbon black, metal, and metal oxide, it is also possible to use a compound called an ionic conductive agent such as an inorganic ion salt or an organic ion salt. Specific inorganic ion salts include perchlorates, chlorates, hydrochlorides, bromates, iodates, borofluoric acid of alkali metals or alkaline earth metals such as lithium, sodium, calcium, and magnesium. Salt, trifluoromethyl sulfate, sulfonate, and the like. Organic ionic salts include aliphatic sulfonates, higher alcohol sulfates, higher alcohol phosphates, higher alcohol ethylene oxide addition sulfates, higher alcohol ethylene oxide addition phosphates, quaternary ammonium salts. Etc. Among these, quaternary ammonium salts are particularly preferred, and specifically, perchlorates and chlorates such as tetraethylammonium, tetrabutylammonium, lauryltrimethylammonium, stearyltrimethylammonium, hexadecyltrimethylammonium, benzyltrimethylammonium and the like. , Hydrochloride, bromate, iodate, borofluoride, sulfate, alkyl sulfate, carboxylate sulfonate, and the like.

As described above, in the present invention, the surface resistance value Rso of the upper layer 12a and the surface resistance value Rsu of the lower layer 12b are:
0.1 ≦ Rsu / Rso ≦ 10.0
It is presumed that the influence of the resistance difference between the upper layer 12a and the lower layer 12b is eliminated and the charge can move smoothly between the layers. As a result, the residual charge does not increase with the progress of image formation, and a print can be created without causing a change in image quality. For example, even in a case where continuous printing is performed at a level of several thousand sheets, residual charges are leaked from the lower layer 12b to the conductive shaft 11, and unnecessary charges do not remain in the resin layer 12, so that the surface of the developing roller (upper layer 12a surface) It is assumed that the potential is always maintained at a constant level. As shown in the embodiments described later, for example, when 3000 sheets are continuously printed, the fluctuation of the surface potential of the developing roller at the start of printing and after 3000 sheets of continuous printing is within 10 V in absolute value. It has become. As described above, according to the present invention, even when continuous printing is performed, it is possible to obtain a printed matter in which the potential on the surface of the developing roller hardly fluctuates and the quality does not vary.

The potential on the surface of the developing roller can be measured by loading the developing roller in the residual potential measuring device shown in FIG. Examples of conditions for measuring the potential on the surface of the developing roller include the following conditions. That is,
Measurement conditions Charger: Corotron Charging current Ic: 850 μA
Charging gap: 1mm
Rotation speed: 240rpm
Measurement environment: 20 ° C, 60% RH
Note that the measurement environment when the residual potential is measured in a low temperature and low humidity environment is 10 ° C. and 20% RH. When measuring the fluctuation of the residual potential accompanying the image formation, first, the developing roller removed from the developing device in the stage before printing is attached to the residual potential measuring device of FIG. 3, and the potential is measured. After the measurement, the developing roller is attached to the developing device, the developing device is set in the image forming apparatus, and a predetermined number of prints are performed. After printing a predetermined number of sheets, the developing roller is removed from the developing device and attached to the residual potential measuring device described above to measure the residual potential. In this way, the fluctuation of the residual potential as the image formation proceeds is confirmed.

  The resin layer 12 forms a toner layer on the surface thereof, charges the toner by frictional charging, and conveys the toner on the surface. Further, the resin layer 12 is required to exhibit a strong adhesive force between the resin layer 12 and the shaft 11.

  An example of a resin that exhibits this performance is, for example, a polyurethane resin obtained by reacting a polyol and an isocyanate. In addition to the polyol and isocyanate, a chain extender may be added as necessary when the polyurethane resin is produced.

  Specific examples of the polyol include polyurethane polyol compounds such as polytetramethylene ether glycol, poly-ε-caprolactone diol, polycarbonate polyol, and polypropylene glycol. Among these, a polycarbonate polyol that forms a polyurethane resin that prevents a decrease in charge amount of the toner during image formation in a high temperature and high humidity environment is preferable. Specifically, aliphatic or alicyclic polycarbonate polyols such as polyhexamethylene carbonate diol are more preferable.

  Specific examples of the isocyanate include 4,4′-diphenylmethane diisocyanate (MDI), cyclohexane diisocyanate, hydrogenated MDI, isophorone diisocyanate, 1,3-xylylene diisocyanate, 2,4-tolylene diisocyanate, 2,6 -Tolylene diisocyanate etc. are mentioned.

  Moreover, it is also possible to use the urethane prepolymer obtained by making it react so that it may have an isocyanate group in the molecular terminal using the said isocyanate, polyol, and also polyamine.

  Examples of the chain extender include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, isophoronediamine (IPDA), hydrazine, and the like. Can be mentioned.

  A typical production method of the polyurethane resin includes a one-stage method and a two-stage method. The one-stage method is a method for producing a polyurethane resin by reacting a polyol, a diisocyanate compound, and, if necessary, a chain extender or a polymerization terminator in a suitable solvent at a time. In the two-stage method, a prepolymer having an isocyanate group at the end of the polyol chain is prepared by reacting a polyol and a diisocyanate compound in an environment where the isocyanate group is excessive, and then this is chain-extended in a suitable solvent. The reaction is performed in an environment in which an agent and a polymerization terminator are present. Among these, the two-stage method has an advantage that a uniform polymer solution can be easily obtained.

  As a solvent used when producing a polyurethane resin, the following are usually mentioned. Aromatic solvents such as benzene, toluene, xylene; ester solvents such as ethyl acetate and butyl acetate; alcohol solvents such as methanol, ethanol, isopropanol, n-butanol, diacetone alcohol; acetone, methyl ethyl ketone, methyl isobutyl ketone, etc. Examples include ketone solvents, other dimethylformamide, dimethylacetamide, ethylene glycol dimethyl ether, tetrahydrofuran, and cyclohexanone. These organic solvents can be used alone or in combination.

  Moreover, the adhesiveness between the resin layer 12 and the shaft 11 can be obtained by including in the resin layer 12 a compound having a molecular structure in which a resin component called a resin-silica hybrid and a silica component are integrated by molecular bonding. It is also possible to improve. The resin-silica hybrid is composed of a region having a network-like silica structure (also referred to as a silica skeleton in the present invention) by alternating bonds of silicon atoms and oxygen atoms, and a region of an organic polymer composed of a polyurethane resin or a vinyl polymer resin. It is comprised from.

  The resin-silica hybrid forms an alkoxy group-containing silane-modified resin by the reaction of a resin having a functional group reactive with an epoxy group and an epoxy group-containing alkoxysilane partial condensate, and condenses the alkoxy group-containing silane-modified resin. It is cured by reaction to form a silica structure.

  Next, the developing roller manufacturing method according to the present invention will be described. The developing roller according to the present invention has a structure in which a resin layer having a two-layer structure is provided around a conductive shaft. The developing roller is coated with a coating liquid containing a resin constituting the resin layer, and is heated after the coating. It is produced by performing.

  An example of the procedure for producing the developing roller according to the present invention will be described below.

  First, a material for forming the lower layer 12b that is one of the resin layers 12 is mixed and dissolved in an organic solvent to prepare a coating solution for forming the lower layer 12b. When preparing the coating solution for forming the lower layer 12b, it is possible to add a conductive material such as carbon black to the coating solution in order to control the electrical characteristics of the lower layer 12b.

  When preparing the coating solution, it is preferable that the components in the coating solution are uniform. For example, when a coating solution is prepared by adding carbon black or the like together with a resin, the carbon black or the like is uniformly dispersed. It is preferable to prepare it. As a means for preparing the coating solution, for example, a sand grinder type dispersion device represented by “Dynomill TILAB (manufactured by Shinmaru Enterprises)” and the like can be mentioned. In the sand grinder type dispersion apparatus, for example, dispersion processing is performed using glass beads having a diameter of 0.5 mm.

  In this manner, a conductive material such as carbon black is uniformly dispersed in the coating solution to prepare a coating solution for forming the lower layer 12b.

  Further, it is possible to select a resin material, a solvent, a conductive material, and the like, and to prepare a coating liquid for forming the upper layer 12a that constitutes the developing roller surface by the same procedure as that for preparing the coating liquid for forming the lower layer 12b. .

  Next, a coating solution for forming the lower layer 12 b is applied on the conductive shaft 11. Various coating methods can be selected according to the viscosity of the coating solution for forming the lower layer 12b. Specific examples of the coating method include a dipping method, a spray method, a roll coating method, and a brush coating method. In the present invention, these coating methods are not limited.

  After applying the coating solution for forming the lower layer 12b on the conductive shaft, drying and heat treatment (for example, temperature: 120 to 200 ° C., processing time: 20 to 90 minutes) are performed, and the solvent in the coating solution for forming the lower layer 12b is removed. By removing, the lower layer 12b is formed. In the present invention, when the lower layer 12b is formed, the surface resistance value Rsu of the lower layer 12b is measured using the surface resistance measuring device 30 of FIG.

  After the lower layer 12b is formed on the conductive shaft 11, the upper layer 12a forming coating solution is applied on the lower layer 12b, and after coating, the coating solution is dried and heated to form the upper layer 12a. As the coating method, drying, and heat treatment method when forming the upper layer 12a, the same methods as those used when forming the lower layer 12b can be used. By forming the upper layer 12a on the lower layer 12b, FIG. A developing roller having a two-layer structure shown in FIG. Then, when the upper layer 12a is formed, the surface resistance value Rso of the upper layer 12a is measured using the surface resistance measuring device 30 of FIG.

  Next, the image forming method according to the present invention will be described. The developing roller according to the present invention is preferably used in an image forming apparatus using a non-magnetic one-component developer that forms an image without using a carrier.

  The developing roller according to the present invention is mounted in a developing device that supplies toner onto an image carrier that forms an electrostatic latent image. The developing device has a toner layer regulating member and a toner replenishing auxiliary member in addition to the developing roller according to the present invention, and these members are arranged so as to contact each other. In the developing device, a thin toner layer is formed on the developing roller by the toner layer regulating member and the toner replenishing auxiliary member, and this is supplied onto the image carrier to visualize the latent image formed on the image carrier. .

  The toner layer regulating member supplies the toner in a uniform thin layer state on the developing roller and frictionally charges the supplied toner. The toner layer regulating member is a member having a certain degree of elasticity, such as urethane rubber or a metal plate, and forms a thin layer of toner on the developing roller by contacting the developing roller. The toner thin layer formed on the developing roller has a maximum thickness of 10 toner particles, preferably 5 or less.

  The pressing force of the toner layer regulating member to the developing roller is preferably 100 mN / cm to 5 N / cm, and particularly preferably 200 mN / cm to 4 N / cm. By setting the pressing force within the above range, toner can be transported without causing transport unevenness, and the occurrence of image defects such as white stripes can be avoided. Further, by setting the pressing force within the above range, the toner is supplied to the developing roller without applying a load that causes deformation or crushing of the toner. The pressing force to the developing roller can be set to a desired size within the above range by adjusting the material constituting the toner layer regulating member and the length and thickness of the member during image formation. is there.

  The toner replenishment auxiliary member is for stably supplying toner to the developing roller. As the toner replenishing auxiliary member, for example, a water wheel-like roller with a stirring blade or a sponge-like roller is used. The size (diameter) of the toner replenishing auxiliary member is preferably 0.2 to 1.5 times the diameter of the developing roller. When the toner replenishing auxiliary member is within this range, the toner is supplied to the developing roller without excess or deficiency, and there is no image defect. Enables good image formation.

  Examples of the image carrier used in the image forming method according to the present invention include inorganic photoreceptors, amorphous silicon photoreceptors, and organic photoreceptors. Among these, organic photoreceptors are particularly preferable, and charge transport is further performed. A layered structure of a layer and a charge generation layer is preferred.

  Hereinafter, a developing device (developing device) that can be used in the image forming method according to the present invention will be described in detail.

  FIG. 4 is a sectional view of the developing device 20 that can be used in the image forming method according to the present invention.

  The developing device 20 shown in FIG. 4 can perform development using a non-magnetic one-component toner (non-magnetic one-component developer). The developing device 20 includes the developing roller 10 according to the present invention, a buffer chamber 22 provided on the left side of the developing roller 10, and a hopper 23 adjacent to the buffer chamber 22. The developing roller 10 is rotationally driven in a counterclockwise direction in the drawing by a motor (not shown), and contacts or approaches an image carrier that is incorporated in an image forming apparatus (not shown).

  In the buffer chamber 22, a blade 24 as a toner regulating member is disposed in pressure contact with the developing roller 10. The blade 24 regulates the charge amount and adhesion amount of toner on the developing roller 10. Further, it is possible to further provide an auxiliary blade 25 for assisting the regulation of the toner charge amount and adhesion amount on the developing roller 10 on the downstream side of the blade 24 with respect to the rotation direction of the developing roller 10.

  A supply roller 26 is pressed against the developing roller 10. The supply roller 26 is rotationally driven in the same direction as the developing roller 10 (counterclockwise direction in the figure) by a motor (not shown). The supply roller 26 has a conductive cylindrical substrate and a foam layer formed of urethane foam or the like on the outer periphery of the substrate.

  The hopper 23 contains toner T which is a one-component developer. The hopper 23 is provided with a rotating body 27 for stirring the toner T. A film-like conveying blade is attached to the rotating body 27, and the toner T is conveyed by the rotation of the rotating body 27 in the direction of the arrow. The toner T conveyed by the conveying blades is supplied to the buffer chamber 22 through a passage 28 provided in a partition wall that separates the hopper 23 and the buffer chamber 22. The shape of the conveying blade is bent while the toner T is conveyed in front of the rotation direction of the blade 27 as the rotating body 27 rotates, and returns to a straight state when the left end of the passage 28 is reached. Thus, the blade T supplies the toner T to the passage 28 by returning the shape straight after passing through the curved state.

  The passage 28 is provided with a valve 281 for closing the passage 28. This valve is a film-like member, one end of which is fixed to the upper side of the right side of the passage 28 of the partition wall. When the toner T is supplied from the hopper 23 to the passage 28, the valve 28 is pushed rightward by the pressing force from the toner T. Can be opened. As a result, the toner T is supplied into the buffer chamber 22.

  In addition, a regulating member 282 is attached to the other end of the valve 281. The regulating member 282 and the supply roller 26 are arranged so as to form a slight gap even when the valve 281 closes the passage 28. The regulating member 282 adjusts so that the amount of toner collected at the bottom of the buffer chamber 22 does not become excessive, so that a large amount of toner T collected from the developing roller 10 to the supply roller 26 does not fall to the bottom of the buffer chamber 22. Adjusted to

  In the developing device 20, the developing roller 10 is rotationally driven in the direction of the arrow during image formation and the toner in the buffer chamber 22 is supplied onto the developing roller 10 by the rotation of the supply roller 26. The toner T supplied onto the developing roller 10 is charged and thinned by a blade 24 and an auxiliary blade 25, and then conveyed to a region facing the image carrier to develop an electrostatic latent image on the image carrier. To be served. The toner that has not been used for development returns to the buffer chamber 22 as the developing roller 10 rotates, and is scraped and collected from the developing roller 10 by the supply roller 26.

  The developing bias power supply 29 provided in the developing device 20 forms an alternating electric field (for example, Vpp is 2.0 kV, frequency 2 kHz) with a DC voltage power source that outputs a set value (for example, about 500 V) of the developing bias voltage Vb. It consists of an AC power supply. “Vpp” indicates a peak-to-peak voltage that is the difference between the peak and valley of the amplitude of the alternating voltage waveform.

  At the time of image formation, the electrostatic latent image carrier 11 is uniformly charged to a potential of, for example, about 800 V by a charging device (not shown), and then a predetermined portion is exposed by an optical head such as a laser. An electrostatic latent image is formed by being attenuated to a potential of about 100V.

  In the developing region, the toner formed in a thin layer on the developing roller 10 flies from the circumferential surface of the developing roller 10 by the action of an electric field formed by the developing bias voltage Vb applied from the developing bias power supply device 29 and an alternating voltage. To become a cloud cloud. Then, toner is supplied onto the electrostatic latent image carrier on which the electrostatic latent image is formed, and the electrostatic latent image is developed to form a toner image.

  The thickness of the toner layer formed on the developing roller 10 is controlled, for example, by setting the following conditions. That is, the peripheral speed of the electrostatic latent image carrier 11 is 100 mm / sec, the peripheral speed of the developing roller 10 is 200 mm / sec, and the pressing force with which the toner regulating member 24 presses the developing roller 10 is 100 mN / cm as described above. It is set to ˜5 N / cm, preferably 200 mN / cm to 4 N / cm. As a result, it is possible to form a toner layer of 10 layers (for 10 toner particles) or less, preferably 5 layers (for 5 toner particles) or less.

  Note that the configuration of the developing device on which the developing roller according to the present invention can be mounted is not limited to that shown in FIG.

  Next, an example of a full-color image forming apparatus in which the developing device 20 shown in FIG. 4 can be mounted is shown in FIG. The image forming apparatus on which the developing device 20 shown in FIG. 4 can be mounted is not limited to the one shown in FIG. In the image forming apparatus shown in FIG. 5, a charging brush 16 for uniformly charging the surface of the photosensitive drum 15 to a predetermined potential and a cleaner 17 for removing residual toner on the photosensitive drum 11 are provided around the photosensitive drum 15 that is rotationally driven. Is provided.

  The laser scanning optical system 18 scans and exposes the photosensitive drum 15 uniformly charged by the charging brush 16 to form an electrostatic latent image on the photosensitive drum 15. The laser scanning optical system 18 includes a laser diode, a polygon mirror, and an fθ optical element, and print data for each of yellow, magenta, cyan, and black is transferred from the host computer to the control unit. Based on the print data of each color, a laser beam is sequentially output, and the photosensitive drum 15 is scanned and exposed to form an electrostatic latent image for each color.

  The developing device unit 30 containing the developing device 20 according to the present invention performs development by supplying each color toner to the photosensitive drum 15 on which the electrostatic latent image is formed. The developing device unit 30 is provided with four developing devices 20Y, 20M, 20C, and 20Bk each containing non-magnetic one-component toners of yellow, magenta, cyan, and black around the support shaft 33. The developing device 20 is guided to a position facing the photosensitive drum 15 by rotating to the center.

  The developing device unit 30 rotates around the support shaft 33 each time an electrostatic latent image of each color is formed on the photosensitive drum 15 by the laser scanning optical system 18 and stores the corresponding color toner. 20 is guided to a position facing the photosensitive drum 15. Then, each of the developing devices 20Y, 20M, 20C, and 20Bk sequentially supplies the charged color toners onto the photosensitive drum 15 to perform development.

  In the image forming apparatus of FIG. 5, an endless intermediate transfer belt 40 is provided downstream of the developing device unit 30 in the rotation direction of the photosensitive drum 15, and is driven to rotate in synchronization with the photosensitive drum 15. The intermediate transfer belt 40 comes into contact with the photosensitive drum 15 at a portion pressed by the primary transfer roller 41 and transfers the toner image formed on the photosensitive drum 15. Further, a secondary transfer roller 43 is rotatably provided so as to face the support roller 42 that supports the intermediate transfer belt 40, and the portion on the intermediate transfer belt 40 is opposed to the support roller 42 and the secondary transfer roller 43. The toner image is pressed and transferred onto the recording material S such as recording paper.

  A cleaner 50 that removes residual toner on the intermediate transfer belt 40 is provided between the developing device unit 30 and the intermediate transfer belt 40 so as to be able to contact and separate from the intermediate transfer belt 40.

  A paper feeding unit 60 that guides the recording material S to the intermediate transfer belt 40 includes a paper feeding tray 61 that houses the recording material S, and a paper feeding roller 62 that feeds the recording material S stored in the paper feeding tray 61 one by one. It comprises a timing roller 63 that feeds the fed recording material S to the secondary transfer site.

  The recording material S on which the toner image is pressed and transferred is conveyed to the fixing device 70 by a conveying means 66 constituted by an air suction belt or the like, and the toner image transferred by the fixing device 70 is fixed on the recording material S. After fixing, the recording material S is transported through the vertical transport path 80 and discharged onto the upper surface of the apparatus main body 100.

Examples of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.
1. 1. Production of developing roller 1-1. Preparation of coating solution (1) Preparation of coating solution 1 Furnace black 30 parts by mass Rutile titanium oxide “GTR-100 (manufactured by Sakai Chemical Co., Ltd.)” having an average particle size of 260 nm
10 parts by mass Methyl ethyl ketone (MEK) 400 parts by mass were placed in the media type disperser “Dynomill TILAB (manufactured by Shinmaru Enterprises)” in the above order, and 100 parts by mass of glass beads having a diameter of 0.5 mm were further added. The primary dispersion was prepared by carrying out a dispersion treatment at 1000 rpm for 2 hours.

Next, in the primary dispersion,
100 parts by mass of urethane resin “Nipporan 5120 (manufactured by Nippon Polyurethane Co., Ltd.)” was added, and dispersion treatment was performed at 1000 rpm to prepare “Coating Liquid 1”.
(2) Preparation of coating liquid 2 Furnace black 20 parts by mass Tetraethylammonium chlorate as quaternary ammonium salt 5 parts by mass Methyl ethyl ketone (MEK) 400 parts by mass Entered into Enterprise Price Co., Ltd.), 100 parts by mass of glass beads having a diameter of 0.5 mm were added, and dispersion treatment was performed at 1000 rpm for 2 hours to prepare a primary dispersion.

Next, in the primary dispersion,
100 parts by mass of urethane resin “Nipporan 5120 (manufactured by Nippon Polyurethane Co., Ltd.)” was added and dispersion treatment was performed at 1000 rpm to prepare “Coating Liquid 2”.
(3) Preparation of Coating Liquid 3 “Coating Liquid 3” was prepared in the same manner as in “Coating Liquid 1” except that the amount of furnace black added was changed to 20 parts by mass.
(4) Production of coating solution 4 “Coating solution 4” was produced in the same manner as in the production of “coating solution 1” except that the addition amount of rutile titanium oxide was changed to 20 parts by mass.
(5) Preparation of coating liquid 5 Furnace black 15 parts by weight Methyl ethyl ketone (MEK) 400 parts by weight was put into a media type disperser “Dynomill TILAB (manufactured by Shinmaru Enterprises)”, and diameter 0.5 mm 100 parts by mass of glass beads were added, and a dispersion treatment was performed at 1000 rpm for 2 hours to prepare a primary dispersion.

Next, in the primary dispersion,
100 parts by mass of urethane resin “Nipporan 5120 (manufactured by Nippon Polyurethane Co., Ltd.)” was added, and dispersion treatment was performed at 1000 rpm to prepare “Coating Liquid 5”.
1-2. Production of Development Rollers 1 to 10 (1) Production of Development Roller 1 “Coating solution 1” is applied to a peripheral surface of a shaft made of SUS303 having a diameter of 10 mm so that the thickness when dried is 15 μm, and is heated at 100 ° C. Was performed for 1 hour to form a lower layer, and the surface resistance value of the lower layer was measured using the circular electrode shown in FIG. 2 and found to be 2.0 × 10 ⁹ Ω / □. Subsequently, “Coating liquid 2” is applied on the lower layer so that the thickness when dried is 15 μm, and the upper layer is formed by performing heat treatment at 100 ° C. for 1 hour, and the two layers are formed on the conductive shaft. “Developing roller 1” having a resin layer was produced. The surface resistance value of the upper layer of the developing roller 1 was measured using the circular electrode and found to be 1.0 × 10 ¹⁰ Ω / □.
(2) Production of developing roller 2 In the production of “developing roller 1”, “developing roller 2” was used for forming the lower layer and “coating liquid 1” was used for forming the upper layer. 2 "was produced. The surface resistance value of the lower layer was 1.0 × 10 ¹⁰ Ω / □, and the surface resistance value of the upper layer was 2.0 × 10 ⁹ Ω / □.
(3) Production of developing roller 3 In the production of “developing roller 1”, “developing roller 3” was used in the same procedure except that “coating liquid 3” was used to form the lower layer and “coating liquid 2” was used to form the upper layer. 3 "was produced. The surface resistance value of the lower layer was 1.0 × 10 ⁹ Ω / □, and the surface resistance value of the upper layer was 1.0 × 10 ¹⁰ Ω / □.
(4) Production of developing roller 4 In the production of “developing roller 1”, “developing roller 4” was used for forming the lower layer and “coating liquid 1” was used for forming the upper layer. 4 "was produced. The surface resistance value of the lower layer was 2 × 10 ⁸ Ω / □, and the surface resistance value of the upper layer was 2 × 10 ⁹ Ω / □.
(5) Production of developing roller 5 “Developing roller 2” was produced in the same manner as in the production of “developing roller 2” except that “coating liquid 2” was used for the upper layer.
(6) Production of developing roller 6 In the production of “developing roller 2”, “developing roller 6” was prepared in the same procedure except that the coating liquid was applied so that the thickness of the upper layer and the lower layer after drying was 8 μm. Produced. The surface resistance values of the upper layer and the lower layer were the same as those of “Developing roller 2”.
(7) Production of developing roller 7 In the production of “developing roller 2”, “developing roller 7” was prepared in the same procedure except that the coating liquid was applied so that the thickness after drying of the upper layer and the lower layer was 22 μm. Produced. The surface resistance values of the upper layer and the lower layer were the same as those of “Developing roller 2”.
(8) Production of developing roller 8 In the production of “developing roller 1”, “developing roller 5” was used for forming the lower layer and “coating liquid 2” was used for forming the upper layer. 8 "was produced. The surface resistance value of the lower layer was 2 × 10 ¹¹ Ω / □, and the surface resistance value of the upper layer was 1 × 10 ¹⁰ Ω / □.
(9) Production of Developing Roller 9 “Developing Roller 9” was produced in the same procedure as in the production of “Developing Roller 8”, except that “Coating Liquid 1” was used to form the upper layer. The surface resistance value of the lower layer was 2 × 10 ¹¹ Ω / □, and the surface resistance value of the upper layer was 2 × 10 ⁹ Ω / □.
(10) Production of developing roller 10 “Developing roller 10” was produced in the same procedure as in the production of “developing roller 1”, except that “coating liquid 5” was used to form the upper layer. The surface resistance value of the lower layer was 2 × 10 ⁹ Ω / □, and the surface resistance value of the upper layer was 2 × 10 ¹¹ Ω / □.

  Table 1 shows the ratio Rsu / Rso of the surface resistance values of the lower layer and the upper layer in “developing rollers 1 to 10” having two resin layers on the conductive shaft produced as described above.

2. Preparation of Toner (1) Preparation of “Resin Particle Dispersion 1” The following compound was charged into a flask equipped with a stirrer and dissolved to prepare a mixed solution, which was further heated to 80 ° C.

Pentaerythritol tetrastearate 72.0 parts by mass Styrene 115.1 parts by mass n-Butyl acrylate 42.0 parts by mass Methacrylic acid 10.9 parts by mass On the other hand, a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction apparatus were attached. In a separable flask, a surfactant solution in which 7.08 parts by mass of an anionic surfactant (sodium dodecylbenzenesulfonate: SDS) was dissolved in 2760 parts by mass of ion-exchanged water was added, and the stirring speed was 230 rpm under a nitrogen stream. The temperature was raised to 80 ° C. with stirring. Next, the mixed solution (80 ° C.) is mixed and dispersed in the surfactant solution (80 ° C.) by a mechanical disperser “CLEAMIX (manufactured by M Technique Co., Ltd.)” having a circulation path. An emulsified liquid in which emulsified particles (oil droplets) having a dispersed particle diameter were dispersed was prepared.

  An initiator solution in which 0.84 parts by mass of a polymerization initiator (potassium persulfate: KPS) was dissolved in 200 parts by mass of ion-exchanged water was added to this dispersion, and this system was heated at 80 ° C. for 3 hours. The polymerization reaction was carried out with stirring. A solution prepared by dissolving 7.73 parts by mass of a polymerization initiator (KPS) in 240 parts by mass of ion-exchanged water was added to the obtained reaction solution, and after 15 minutes, the temperature was adjusted to 80 ° C., followed by mixing comprising the following compounds: The solution was added dropwise over 100 minutes.

Styrene 383.6 parts by weight n-butyl acrylate 140.0 parts by weight Methacrylic acid 36.4 parts by weight n-octyl mercaptan 12 parts by weight The system is heated and stirred at 80 ° C. for 60 minutes and then cooled to 40 ° C. Thus, a resin particle dispersion containing wax (hereinafter referred to as “latex (1)”) was produced.
(2) Preparation of “Colorant Dispersion Liquid K” On the other hand, 9.2 parts by mass of sodium n-dodecyl sulfate was stirred and dissolved in 160 parts by mass of ion-exchanged water. While stirring this solution, 20 parts by mass of carbon black “Mogal L” (Cabot Corp.) was gradually added as a colorant, and then a mechanical disperser “Claremix” (M Technique Co., Ltd.) was added. Using the dispersion treatment, “Colorant Dispersion Liquid K” was prepared. When the particle diameter of the colorant particles in “Colorant Dispersion Liquid K” was measured with an electrophoretic light scattering photometer “ELS-800” (manufactured by Otsuka Electronics Co., Ltd.), the weight average particle diameter was 120 nm.
(3) Preparation of “colored particles K” In a reaction vessel equipped with a temperature sensor, a cooling pipe, a stirring device (having two stirring blades, an intersection angle of 20 °), and a shape monitoring device,
"Latex (1)" 1250 parts by mass (solid content conversion)
Ion-exchanged water 2000 parts by mass “Colorant Dispersion Liquid K” The whole amount was charged, the internal temperature was adjusted to 25 ° C., and 5 mol / liter sodium hydroxide aqueous solution was added to the dispersion liquid mixture to adjust the pH to 10.0. Adjusted.

  Next, an aqueous solution in which 52.6 parts by mass of magnesium chloride hexahydrate was dissolved in 72 parts by mass of ion-exchanged water was added over 10 minutes at 25 ° C. with stirring. Thereafter, the temperature increase was started immediately, and this system was heated to 95 ° C. over 5 minutes (temperature increase rate: 14 ° C./min).

  In this state, the particle size of the aggregated particles was measured with “Multisizer 3 (manufactured by Beckman Coulter)”. When the volume-based median diameter (D50) reached 6.5 μm, 115 parts by mass of sodium chloride was ionized. Particle growth was stopped by adding an aqueous solution dissolved in 700 parts by mass of exchange water. Furthermore, after heating and stirring (stirring rotation speed 120 rpm) for 8 hours at a liquid temperature of 90 ° C. and continuing aging, the system was cooled to 30 ° C. at 10 ° C./min. Was added to adjust the pH to 3.0, and stirring was stopped.

The produced particles are filtered, washed repeatedly with ion-exchanged water, classified in liquid with a centrifugal separator, and then dried using a flash jet dryer to give “colored particles K” having a water content of 1.0 mass%. Was generated.
(4) Preparation of “Toner K” In the above “colored particles K”, 0.8 part by mass of hydrophobic silica having a number average primary particle size of 12 nm and a hydrophobization degree of 65, a number average primary particle size of 30 nm, and hydrophobic 0.5 parts by weight of hydrophobic titania having a degree of conversion of 55 was added and mixed with a Henschel mixer to prepare “Toner K”.
3. Evaluation Experiment A commercially available color laser printer “Magicor 5440DL (manufactured by Konica Minolta Business Technologies Co., Ltd.)” was mounted with the developing rollers 1 to 10 and the developing device containing the toner for evaluation. Under development conditions, Vb was set to 420 V, Vpp was set to 1100 V, and the frequency of the alternating electric field was set to 2.0 kHz. As shown in Table 1, the developing rollers (developing devices) 1 to 10 were designated as Examples 1 to 7 and Comparative Examples 1 to 3.

  Evaluation was performed for 3000 continuous prints in a low-temperature and low-humidity environment (10 ° C., 20% RH), and after continuous printing, residual potential fluctuations, fogging, density unevenness, white spots, and in-machine stains were performed. The print image used for continuous printing is an image with a pixel ratio of 6% on the print, and a halftone image, a human face photo, a white background image, and a solid image with a reflection density of 0.80 are each 1/4. An equally divided A4 size image is output.

<Residual potential of developing roller>
Before the continuous printing, the developing roller was set in the residual potential measuring device of FIG. 3 placed in a low temperature and low humidity environment (10 ° C., 20% RH), and the residual potential of the developing roller before the printing was measured. After continuous printing, the developing roller was taken out from the developing device loaded in the image forming apparatus, and the residual potential of the developing roller after continuous printing was measured by the residual potential measuring device. Those having a potential difference of 10 V or less before and after the continuous printing were regarded as acceptable.

<Fog>
A halftone image, a human face photograph, and a white background image on three print images from the 2998th sheet to the 3000th sheet were visually evaluated to evaluate the occurrence of fog. Evaluation: O: No occurrence of fog and no problem △: Slight occurrence of fog on white background, but not observed on halftone image or human face photo image ×: On three images The occurrence of fog was confirmed, and ○ and Δ were accepted.

<Density unevenness>
Evaluation was performed using a halftone image and a solid image in which the reflection density in the three print images from the 2998th sheet to the 3000th sheet was 0.80. Select any 7 points on each image, measure the reflection density using a Macbeth reflection densitometer (RD-918), calculate the difference between the maximum density and the minimum density, and calculate the average value of the three images. The density unevenness was evaluated by taking The smaller the difference between the maximum density and the minimum density, the smaller the density unevenness. A case where the density difference in the halftone image was 0.05 or less and the density difference in the solid image was 0.15 or less was accepted.

<Outline>
The evaluation was performed on the halftone image portion and the solid image portion on the evaluation image output after the printing of 3000 sheets. The number of white spots with a major axis of 0.4 mm or more was determined on the A4 sheet, and less than 20 passed, especially those with 3 or less white spots were evaluated as excellent. The major diameter of the white spots is measured with a microscope with a video printer.

<In-flight dirt>
The state of contamination in the apparatus due to toner spillage from the developing device after 3000 sheets of continuous printing was visually evaluated, and the degree of soiling of the hand when the developing device was removed from the image forming apparatus was evaluated. The following four ranks were classified and judged.

◎: No toner adherence to the upper lid of the developing device or in-machine dirt inside the device, and even when the developing device was removed, the hands were not soiled at all. ○: In the developing device, a slight amount of toner adhered to the upper lid near the developing roller. In other locations, toner adhesion is not observed. Also, there was no toner scattering inside the device, and even when the developing device was removed, the hands did not get dirty. Δ: Toner adhered to a part of the upper lid of the developing device, but no toner scattering inside the device was seen and development Even if the apparatus was removed, the hands did not get dirty. ×: Toner scattering into the machine was confirmed, and when the developing apparatus was removed, the hands became dirty to the extent that hand washing was necessary.

  The results are shown in Table 2.

  As shown in Table 2, in Examples 1 to 7 equipped with the developing roller corresponding to the present invention, the fluctuation of the residual potential on the surface of the developing roller before and after continuous printing of 3000 sheets was at a level where there is no problem. Further, even when continuous printing was completed, image defects such as fogging, density unevenness, and white spots were not seen on the printed image, and stable image formation was possible and no internal contamination was observed. On the other hand, it was confirmed that Comparative Examples 1 to 3 did not yield results satisfying all the items in the evaluation items, and the effects of the present invention were not exhibited.

It is sectional drawing of the developing roller which concerns on this invention. It is a block diagram of the surface resistance measuring apparatus which measures the surface resistance value of a developing roller. It is the schematic of the surface potential measuring apparatus of a developing roller. It is sectional drawing of the developing device which can mount the developing roller which concerns on this invention. FIG. 3 is a cross-sectional view of a full-color image forming apparatus in which the developing roller according to the present invention can be used.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Developing roller 11 Conductive shaft 12 Resin layer 12a Upper layer 12b Lower layer 20 Developing device 30 Surface resistance measuring device 31A, 31B Electrode roller 32 DC power supply 33 Ammeter

Claims (2)

A developing roller having two resin layers around a conductive shaft,
Among the resin layers, when the surface resistance value of the layer constituting the developing roller surface is Rso and the surface resistance value of the layer adjacent to the conductive shaft is Rsu,
0.1 ≦ Rsu / Rso ≦ 10.0
A developing roller having the following relationship: A step of carrying toner on the surface of a developing roller provided with two resin layers around a conductive shaft, supplying the carried toner onto the image carrier, and developing an electrostatic latent image on the image carrier; An image forming method comprising:
The developing roller for supplying toner onto the image carrier;
Among the resin layers, when the surface resistance value of the layer constituting the developing roller surface is Rso and the surface resistance value of the layer adjacent to the conductive shaft is Rsu,
0.1 ≦ Rsu / Rso ≦ 10.0
An image forming method having the following relationship:

Images