JP2005316144A - Conductive roller for electrophotography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive roller which substantially prevents the occurrence of density unevenness in an output image in spite of deterioration by continuous use and which has an excellent resistance characteristic. <P>SOLUTION: The conductive roller for electrophotography is characterized by satisfying (S2/S1)/I≤3.0 (I is an average value of the measurement current.) when the current value measured by rotating the conductive roller for electrophotography of a radius r at a fixed period (n times/second) is defined as I, the summation of the total frequency component of the current fluctuation in the current as S1, and the sum of the components of the frequencies 3 nr/8 to 3 nr/4 Hz as S2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic conductive roller.

  Conventionally, as one of latent image developing methods in electrophotographic apparatuses such as printers and copiers, for example, a one-component developing method disclosed in Patent Document 1 and Patent Document 2 is known. A developing method using an (elastic body) roller is disclosed.

  In the image forming process, an electric charge is generated on the surface of the image forming body using a contact-type charging roller. An electrostatic latent image is formed on the surface of the image forming body by neutralizing a part of the generated charges.

  The toner is conveyed onto the image forming body using a developing roller. The electrostatic latent image is developed by bringing the developing roller into contact with or close to the surface of the image forming body while the toner is carried on the surface.

  For the conductive roller used in these steps, it is necessary to supply a uniform charge to the image forming body or to develop the toner on the image forming body without unevenness. In this case, it is required to always be in contact with or in close proximity with a predetermined discharge area or development area that is stable. Further, in the case of the developing roller, it is necessary to uniformly bring the layer thickness regulating member into contact with the surface thereof, so that the toner is thinned and is uniformly carried on the roller surface.

  Stable physical properties are indispensable for uniform charging and development with toner, and lack of them causes various image defects such as uneven density of the roller pitch. For this reason, various proposals have conventionally been made as physical characteristics to be satisfied by the conductive roller. As one of typical management characteristics, for example, Patent Document 3 discloses managing roller resistance.

  However, due to remarkable progress in recent years such as speeding up of electrophotographic apparatuses and higher quality of image quality, the characteristics required of conductive rollers have become more advanced, and the resistance of the rollers found in Patent Document 3 has been increased. It is becoming strict to meet the demands for speeding up the electrophotographic apparatus, improving the quality of image quality, etc. only by managing. In order to meet the demands for high-speed electrophotographic equipment, high quality image quality, etc., even if we aim to maintain the quality with only the size of the resistance, the limit of the resistance becomes too tight and impractical. The level has been reached.

  In addition, considering the change in characteristics due to roller deterioration, even if the initial resistance is controlled, local density unevenness may occur in the output image while many images are being output. Even exist.

In recent years, there has been a demand for conductive rollers that completely solve this difficult problem. However, considering the manufacturing efficiency and cost of conductive rollers, and changes in characteristics due to deterioration, the problem can be solved by managing only the magnitude of resistance. Is extremely difficult. Therefore, the required characteristics of the conductive roller should be incorporated into the product after reviewing the influence of deterioration in a form that is not excessively limited as much as possible. So I thought.
JP 52-125340 A Special registration No. 2879962 JP-A-11-311898

  In view of the above situation, an object of the present invention is to provide a conductive roller having excellent resistance characteristics that is less likely to cause density unevenness in an output image even by deterioration due to continuous use. More specifically, it is an object of the present invention to provide a conductive roller that does not cause density unevenness in an output image due to an extreme resistance change mainly caused by adhesion of paper dust or toner to the roller surface.

  The present invention was measured when an electrophotographic conductive roller having a radius r was brought into contact with a virtual drum having one or more electrodes having a width of 2 cm at a constant pressure and rotated at a constant period (n times / second). The average value of the current corresponding to the number of rotations of the roller is defined as a current value I (μA), the current fluctuation corresponding to the fluctuation of the current is subjected to frequency conversion, and the obtained frequency waveform is integrated over the entire frequency range. The sum of the frequency components is S1, and when the sum of the components of frequencies 3 nr / 8 to 3 nr / 4 Hz by similar integration is S2, (S2 / S1) /I≦3.0 is satisfied. The electrophotographic conductive roller.

  It has been found that, by satisfying the above conditions, it can withstand deterioration due to continuous use, does not cause density unevenness in the output image, and can be manufactured with maximum production efficiency.

  If the combined characteristics of current fluctuation and current value are adjusted appropriately, the image characteristics will not deteriorate easily even with continued use. A conductive roller can be obtained.

  The inventors of the present invention have been studied to solve the above problems. As a result of investigation, it became clear that the method of specifying the upper and lower limits of resistance makes it difficult to achieve the optimum range when pursuing performance, but it is not always possible to set sufficient conditions when considering deterioration. did.

  An object of the present invention is to suppress not only image characteristics at the initial stage but also density unevenness due to deterioration, that is, unevenness of an output image caused as a result of deposits such as paper dust and toner on the roller surface. Therefore, the ease of occurrence of unevenness of adhesion of paper dust, toner, etc. to the roller surface must be able to be predicted without physical excess or deficiency.

  The present inventors consider that the difference in the state of the roller surface changed by the deposit is recognized as a definite density difference in the output image, and as a result of further investigation, the resistance of the conductive roller before use is reduced. It has been found that the density unevenness described above can be avoided if only the resistance unevenness within a certain range is localized.

  If a region having a high resistance exists locally, electric charges are likely to accumulate in the region, and charged paper powder, toner, and the like are more likely to adhere. When a partial amount of adhesion occurs, the portion where the adhesion occurs further increases in resistance, and the adhesion is further promoted. The peripheral portion also shows an increase in resistance due to the same adhesion, but the resistance difference with the portion with the highest resistance increases on the contrary. As a result, the difference in the adhesion amount further increases, and finally, the electrostatic charge image on the image forming body and the development of the electrostatic latent image with the toner are not uniformly performed.

  If the conductive roller is designed after quantitatively grasping the boundary where such a phenomenon occurs, the produced roller can withstand deterioration due to continuous use, and the output image can be manufactured with maximum production efficiency without causing density unevenness. I found out that it would be something.

  FIG. 1 is a principle diagram for measuring the electrophotographic conductive roller of this embodiment. In actual measurement, a virtual drum divided in the axial direction of the roller must be used in order to examine local unevenness of resistance, but a virtual drum made of a conductor is used over the entire surface for simple explanation.

  FIG. 1A is a conceptual diagram of a measuring apparatus that measures the resistance of a conductive roller for electrophotography (hereinafter sometimes abbreviated as a roller or a conductive roller). After the electrophotographic conductive roller is disposed so as to contact the virtual drum (conductor), a certain weight is applied to the metal shaft core exposed at both ends of the electrophotographic conductive roller. A constant voltage power source and an ammeter are arranged in series between the metal shaft body of the electrophotographic conductive roller and the virtual drum (conductor). When the roller rotates in this state, if the roller resistance is uniform over the entire circumference, a constant current is observed as shown by the straight line in FIG. However, in reality, the resistance of the roller is not uniform, so the current fluctuates as shown by the dotted line. FIG. 1C is a cross-sectional view taken along the line A-A ′ of FIG. As can be seen from FIG. 1C, the current measures the resistance of the shaded portion where the roller at a certain time contacts the virtual drum. That is, the fluctuation of the current having periodicity is nothing but the circumferential resistance unevenness of the roller.

  When the conductive roller has localized resistance unevenness, large current fluctuation is observed. It is considered that the deposits adhere more to the places where the resistance is large. However, if the period of the current fluctuation is gentle over the entire circumference of the roller, there is no steep change in the adhesion amount that can be visually recognized as density unevenness. On the other hand, if the current fluctuation period is small, the resistance unevenness is generally small and it is difficult to appear as a density difference.

  Therefore, the unevenness of resistance of the roller that causes density unevenness in the output image due to adhesion has a large period, but the period is smaller than the gentle unevenness of the resistance over the entire circumference of the roller, and the period is small. The size of the unevenness seems to have an intermediate period and size that is larger than the small resistance unevenness.

  The period of current fluctuation caused by resistance unevenness having an intermediate size and period reflects the circumference of the roller cross section, and is a function having the rotation speed and radius of the roller as variables.

  On the other hand, it is necessary to pay attention to the magnitude of the resistance, that is, the current value. The larger the current value, the easier the diffusion of charges, and thus the local difference in adhesion amount hardly occurs, and the local density unevenness is avoided. It becomes easy.

  FIG. 2 (a) is a conceptual diagram of a measuring apparatus for measuring current fluctuation according to the present invention. A current flowing through a roller (not shown) to which a constant voltage is applied from a constant voltage power source (not shown) is monitored by an ammeter. The current waveform obtained by the ammeter is developed into a composite function obtained by synthesizing waveforms of a plurality of different frequency components by, for example, Fourier transform or the like by a waveform expansion device. The developed waveforms of a plurality of different frequency components are stored in the storage device. The storage device also stores the rotational speed of the roller and the radius of the roller. Next, information on the waveform of a plurality of developed different frequency components is extracted from the information stored in the storage device. Since these have coefficients determined for each frequency component, these coefficients can be arranged and plotted in the frequency space. The waveform thus plotted is shown in FIG. By integrating the plotted frequency waveform over all frequencies, the sum of current fluctuations over all frequencies can be obtained. Similarly, the arithmetic unit calculates the sum of fluctuations of current having an intermediate period between the gentle fluctuation of the current over the entire circumference of the roller and the fluctuation of the current having a small period. In this case, the region to be integrated is the range indicated by the oblique lines in (b).

  Based on this, the inventors have determined that the radius r (mm) of the roller, the rotation speed of the roller (n times / second), the current value is I (μA), the sum of all frequency components of the current fluctuation is S1, the frequency Continuing to satisfy (S2 / S1) /I≦3.0, where S2 is the sum of components from 3 nr / 8 to 3 nr / 4 Hz and the ratio of S2 to S1 is (S2 / S1) (%) It has been found that it is possible to produce a roller that can withstand deterioration due to use and hardly cause density unevenness in an output image. The current value I is an average value of current measured by rotating the roller.

  The electrophotographic conductive roller of this embodiment can be used as a developing roller in an electrophotographic apparatus.

  The conductive roller of the present invention has a structure in which a metal shaft core, an elastic layer containing at least a conductive filler is disposed on the shaft core, and one or more coating layers are disposed on the outer periphery of the elastic layer. I am doing. This coating layer is expected to prevent drum contamination from the elastic body, improve charging characteristics, or prevent paper dust / toner adhesion, etc. It is not.

  The metal shaft core of the conductive roller uses a cylinder having a surface of carbon steel alloy with industrial nickel plating having a thickness of 5 μm. As other materials for the metal shaft core, for example, metals such as iron, aluminum, titanium, copper and nickel, and alloys such as stainless steel, duralumin, brass and bronze containing these metals may be used. it can. Further, the metal shaft core body is not a mere column, but may have a cylindrical shape with a central portion as a cavity.

  In manufacturing the conductive roller in the present invention, first, an elastic layer containing a conductive filler is disposed on the outer periphery of the metal shaft core. For the elastic layer, it is desirable to use a material capable of obtaining an appropriate low hardness and low compression set, and any material can be used as long as this object can be achieved.

  Silicone rubber is one that satisfies the above characteristics. When this is used, the silicone rubber main component is dissolved, an appropriate amount of conductive filler is added, and the same silicone rubber curing agent is added and kneaded to incorporate a metal shaft core. It is molded by a known method such as injection into a molding machine and heating.

  The molecular weight of the rubber used for the conductive elastic layer is not particularly limited, and it is contained from low molecular weight (oligomer) to high molecular weight. Such rubber can be obtained from a manufacturer and used.

  Various commonly used compounding agents can be added to the rubber as long as the characteristics of low hardness and low compression set are not impaired. These blends may be added in the process of producing the elastic layer material, if necessary. For example, natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber, (meth) acrylonitrile butadiene rubber, ethylene propylene rubber, ethylene propylene diene rubber, butyl rubber, halogenated butyl rubber, silicone rubber, fluorine rubber, urethane rubber, Examples thereof include ethylene vinyl acetate copolymer, ethylene- (meth) acrylate rubber, epichlorohydrin rubber and the like.

Examples of the reinforcing filler and extender to be added include conductive carbon black, conductive filler, conductive plasticizer, ion conductive materials such as KSCN, LiClO ₄ , NaClO ₄ and quaternary ammonium salts, fumed Silica, wet silica, quartz fine powder, diatomaceous earth, carbon black, zinc oxide, basic magnesium carbonate, activated calcium carbonate, magnesium silicate, aluminum silicate, titanium dioxide, talc, mica powder, aluminum sulfate, calcium sulfate, sulfuric acid Mention may be made of barium, glass fibers, organic reinforcing agents and organic fillers. The surface of these fillers may be hydrophobized by treatment with an organosilicon compound such as polydiorganosiloxane.

  As the plasticizer, for example, polydimethylsiloxane oil, diphenylsilanediol, trimethylsilanol, phthalic acid derivative, adipic acid derivative and the like can be used. As the softening agent, for example, lubricating oil, process oil, coal tar, castor oil can be used. Other anti-aging agents include phenylenediamines, phosphates, quinolines, cresols, phenols, dithiocarbamate metal salts, etc., and heat-resistant agents include iron oxide, cerium oxide, potassium hydroxide, iron naphthenate, naphthene Potassium acid can be used, and other processing aids, colorants, ultraviolet absorbers, flame retardants, oil resistance improvers, foaming agents, scorch inhibitors, tackifiers, lubricants, and the like can be added.

  As the conductive filler, for example, metal powders and fibers such as aluminum, palladium, iron, copper, and silver can be used, and metal oxides such as carbon black, metal powder, titanium oxide, tin oxide, and zinc oxide can be used. Or metal compound powders such as copper sulfide and zinc sulfide may be used. Furthermore, tin oxide, antimony oxide, indium oxide, molybdenum oxide, and zinc, aluminum, gold, silver, copper, chromium, cobalt, iron, lead, platinum, rhodium are electrolyzed, spray coated, Powders adhered by mixed shaking can also be used, and carbon powders such as acetylene black, ketjen black, PAN-based carbon black, and pitch-based carbon black can also be used.

  Carbon black is particularly preferable as the conductive filler. The electrical resistivity can be reduced by adding a small amount, and conductivity can be imparted without increasing the hardness of the rubber composition. Examples of carbon black brands include Ketjen Black EC, Ketjen Black EC600JD (both manufactured by “Ketjen Black International”), and the like.

  It is necessary to adjust the concentration of the conductive filler appropriately. For example, 2-50 mass% is good. More preferably, it is 5-30 mass%. If the conductive material is small, the variation of the electrical resistivity of the rubber composition is large. It becomes difficult to control the electrical conductivity, for example, it is difficult to adjust the electrical resistivity and uniform dispersion is difficult. Moreover, when too much, rubber | gum will become hard and it is unpreferable.

  In the molding machine for forming the elastic layer, it is more desirable that the liquid rubber injection portion has a rubber reservoir portion having a cylindrical and unbroken structure corresponding to the pipe mold. In this way, the liquid rubber that has passed through the piece gate hole is spread uniformly and uniformly in a cylindrical shape, and then injected into a pipe mold, where it can be thermally cured to form an elastic layer with very little resistance unevenness. This is advantageous when manufacturing a high-resistance material.

  One or more coating layers are disposed on the outer periphery of the conductive bullet layer formed as described above. Examples of the material for forming the coating layer include various polyamides, fluorine resins, hydrogenated styrene-butylene resins, urethane resins, silicone resins, polyester resins, phenol resins, imide resins, and olefin resins. When the coating layer is formed from a urethane resin, the physical properties can be changed over a wide range by changing the structure and blending ratio of the polyol and diisocyanate in various ways.

  When an isocyanate for urethane resin is used as a material for forming the coating layer of the conductive roller, a difunctional or trifunctional isocyanate and a modified isocyanate are usually used. Among these aromatic compounds, 1,5-naphthalene diisocyanate, 2,4- / 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, m- / P-xylylene diisocyanate, which includes isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate for alicyclic groups, and 1,6-hexamethylene diisocyanate and lysine di for aliphatic groups. An isocyanate and 1,6,11-undecane triisocyanate are mentioned.

  Examples of the polyol for urethane resin include polyether, polyester, polybutadiene polyol, acrylic polyol, saponified ethylene-vinyl acetate copolymer having 2 to 3 functionalities and number average molecular weight of several hundred to several thousands. By adjusting the functionality and number average molecular weight of these isocyanates and polyols, desired physical properties such as elasticity can be imparted to the surface of the conductive roller.

  The materials constituting these coating layers are dispersed using a conventionally known dispersing device such as a dispersing device using beads such as a sand mill, a paint shaker, a dyno mill, a pearl mill, or a visco mill, or a dispersing device using a ball mill. The obtained coating material for forming the coating layer is applied to the surface of the conductive elastic layer by a spray coating method, a dipping method or the like. The thickness of the coating layer is preferably 5 to 500 μm, particularly preferably 5 to 30 μm. If the thickness is too small, the photoreceptor may be contaminated by the seepage of low molecular weight components in the base layer, and if it is too thick, the conductive roller becomes hard, which is not preferable because it causes poor fusion and recovery of set marks.

  Fine particles having an average particle diameter of 1 to 50 μm may be dispersed in the coating layer formed as described above, whereby the surface of the conductive roller has an appropriate roughness and is difficult to stick to an image forming body or the like. In the case of a developing roller, the toner can be easily transported and a sufficient amount of toner can be supplied to the developing area. Examples of the fine particles used for such purpose include plastic pigments such as polymethyl methyl methacrylate fine particles, silicone rubber fine particles, polyurethane fine particles, polystyrene fine particles, amino resin fine particles, and phenol resin fine particles. Methyl acid fine particles, polyurethane fine particles, and silicone rubber fine particles are preferred. These fine particles are preferably added in the range of about 5 to 200% by mass of the coating layer.

  If the desired surface properties can be obtained, the coating layer may be one layer or two or more layers. In the case of achieving a plurality of functions such as prevention of drum attack and prevention of toner adhesion to the surface, it may be easier to design two or more layers.

  Whether or not the conductive roller thus obtained satisfies the required resistance characteristics can be examined by using, for example, a measuring machine shown in FIG. In the measuring machine, three electrodes 3 having a width of 2 cm are arranged on the virtual drum 2 of φ30 side by side in the axial direction so that the resistance can be measured at three positions in the roller axial direction. It exists and the voltage at both ends is read with a voltmeter. By simultaneously applying a voltage to this measuring machine, the voltage at three locations is simultaneously read and converted into a current value. At that time, the conductive roller is in close contact with a weight of 500 gW per side at both ends of the metal shaft core. The virtual drum is driven and rotated at such a speed that the rotation period of the conductive roller rotated by the follow is 1 sec, and the resistance unevenness of the conductive roller is measured at three positions in the axial direction in the form of current fluctuation.

Of the current fluctuations, components such as bandpass filters may be used to extract components having a frequency of 3r / 8 to 3r / 4Hz with respect to the roller radius r (mm), or current data is subjected to Fourier transform processing. Also good.
(Examples and Comparative Examples)
Hereinafter, the effects of the present invention will be clarified by showing examples and comparative examples, but the present invention is not limited to the following examples.

  As the conductive filler-containing elastic body in this example and comparative example, dimethylpolysiloxane is used as the main component of the silicone rubber, and dimethylhydrogenpolysiloxane is used in an equal amount as the curing agent. 10 parts by mass of ketjen black is added to 100 parts by mass of the rubber, and 30 parts by mass of the filler is mixed. Molding is performed by injecting them into a molding machine in which a metal shaft core is incorporated and preheating at 100 ° C., curing, cooling and demolding, and then heating again to perform secondary curing. For the rubber injection part, a piece having nine injection holes was prepared so as not to cause unevenness as much as possible, and a 7-hole, a 5-hole, and a 3-hole were prepared for comparison. Also, as a countermeasure against unevenness, a rubber reservoir having a continuous structure is provided in the subsequent stage of the injection port, and there are no reservoirs for comparison and those having only a semi-cylindrical reservoir. Combined. As a result, the unevenness of resistance was given diversity by the elastic layer containing the conductive filler.

  First, 100 parts by mass of an ester polyurethane resin composed of polyester polyol and toluene diisocyanate is dissolved in MEK, and 10 parts by mass of ketjen black and 12 parts by mass of ketjen black are added as the coating layer. Mix each. Each is dispersed with Viscomil for 5 hours, and then 45 parts by mass of urethane particles having an average particle diameter of 6 μm are added and dispersed again for 2 hours. The film thickness of the solution can be adjusted by appropriately adjusting the viscosity and the pulling speed. The solution was coated by immersing and lifting the conductive filler-containing elastic layer disposed on the metal shaft core. With this coating layer, two types of rollers having current values were produced.

  The produced roller is a developing roller having a metal shaft core diameter of 8 mm and a roller diameter of 16 mm. A weight is applied to both ends of the metal shaft core body, and it is desirable that the roller is sufficiently in close contact with the virtual drum and that the roller is not extremely deformed by this weighting. As a range, 300 gW to 800 gW on one side seems to be appropriate, but this time, a load of 500 gW on each side is applied to make contact with the virtual roller. Measured when a voltage of 200 V is applied to the metal shaft core and the electrode of the roller by rotating at a cycle of 1 sec and arranging electrodes of 2 cm width at three positions on both ends and the center of the virtual drum. The current is measured, the average value current I (μA), the current fluctuation at that time is S1, the sum of all frequency components is S1, the sum of the components of the frequency 3r / 8-3r / 4Hz is S2, and (S2 / S1) / I is Calculated. Since the current value of the roller is on the order of μA and the resistance is very large, the accuracy was ensured by measuring the voltage across the reference resistance and converting it into a current, instead of directly measuring with an ammeter. In addition, as shown in (b), the virtual drum draws current flowing from three electrodes to the outside of the drum, and the brass V-shaped block is pressed by the spring to the drawn outer electrode. The sex is secured. Thereby, the current fluctuation is detected without picking up excessive noise.

  The calculated values are listed in the examples in Table 1 and the comparative examples in Table 2. These values are the maximum values measured at three locations, and the pitch unevenness is most likely to occur at the position where the maximum value is recorded.

  After measuring the fluctuation of the current, the roller is incorporated into an electrophotographic printer cartridge as a developing roller, and the printer prints 4000 sheets by outputting one image and stopping for 1 second. It was investigated whether local density unevenness occurred in the output image.

With the black cartridge after outputting 4000 images, the evaluation image was examined for the presence or absence of local density unevenness of the D roller pitch. The evaluation column for local density unevenness is classified as follows.
O: Density unevenness was not observed. Δ: Local density unevenness of a slight D roller pitch was recognized in 600 dpi halftone. X: Local density unevenness of the D roller pitch was conspicuous in 600 dpi halftone.

FIG. 3 is a principle diagram for measuring the electrophotographic conductive roller according to the present invention. The conceptual diagram of the measuring apparatus which measures the fluctuation | variation of the electric current of this invention. The schematic of the electric current fluctuation measuring apparatus of the conductive roller used in the Example and comparative example of this invention.

Explanation of symbols

1 Conductive Roller 2 Virtual Drum 3 Electrode 4 Reference Resistance 5 Electrode A
6 Electrode B
7 Electrode C
8 Current collector connected to electrode A 9 Current collector connected to electrode B 10 Current collector connected to electrode C 11 Conductive roller 12 Resin part

Claims (2)

The current value I, which is an average value of the current measured by rotating the electrophotographic conductive roller having a radius r at a constant cycle (n times / second), and the total sum of all frequency components by frequency conversion of the current fluctuation of the current. A conductive roller for electrophotography characterized by satisfying (S2 / S1) /I≦3.0, where S1 is S1 and the sum of components of frequencies 3 nr / 8 to 3 nr / 4 Hz is S2. An electrophotographic apparatus using the electrophotographic conductive roller according to claim 1 as a developing roller.

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