JP2006145678A - Belt for electrophotography and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt for electrophotography and an image forming apparatus by which high picture quality free of image problems relative to a fine discharging phenomenon such as polka-dotted image ommission and striped density unevenness and phenomena such as scattering and density unevenness in belt pitch for electrophotography can be obtained and an excellent image can be obtained even when an environment changes in a short period. <P>SOLUTION: In the belt for electrophotography used for the electrophotographic image forming apparatus which develops an electrostatic latent image formed on a photoreceptor with a developer and transfers the obtained visual image onto a transfer material after applying a voltage to it, the belt for electrophotography being characterized in that the belt contains at least thermoplastic resin and a conductive agent, which is made principally of carbon in a fine fibrous state and has a 0.1 to 1 μm mean diameter and a ≥1 μm mean length ≥10 times as large as the diameter. The image forming apparatus has the belt for electrophotography. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic belt and an electrophotographic image forming apparatus, and more particularly to a copying machine, a printer, and the like using an electrophotographic system.

  An image forming apparatus using an electrophotographic belt such as an intermediate transfer belt or transfer / conveying belt sequentially stacks and transfers multiple component color images of full-color image information and multi-color image information to synthesize and reproduce full-color images and multi-color images. The present invention is effective as a full-color image forming apparatus or multi-color image forming apparatus that outputs an image formed product, or an image forming apparatus having a full-color image forming function or a multi-color image forming function.

For example, a full-color image forming apparatus having an image forming apparatus using an intermediate transfer belt or the like is an image in which a transfer material is pasted or adsorbed on a transfer drum, which is a conventional technique, and an image is transferred from the electrophotographic photosensitive member thereto. Compared to a full-color image forming apparatus having a forming apparatus, it is possible to transfer an image from an intermediate transfer belt without requiring processing (for example, gripping, adsorbing, giving a curvature, etc.) to a transfer material. envelopes, postcards, label paper or the like, thin to the paper (40 g / ^{m 2} paper) from thick paper (200 g / ^{m 2} paper), wide and narrow width, regardless of the length of long, selecting a transfer material great variety Has the advantage of being able to

  Furthermore, a method of arranging a plurality of electrophotographic photosensitive members corresponding to the required number of colors, transferring the toner image directly onto the intermediate transfer belt in one pass, superimposing the respective colors, and transferring them to the transfer material at once. It is the same until a plurality of electrophotographic photoconductors are arranged, but there is also a method in which the transfer material is supported by a transfer conveyance belt, images of each color are continuously transferred to the transfer material, and the colors are superimposed. These means are effective as means for greatly improving the printing speed. However, in the case of such a transfer system, there is a problem that if the electrophotographic belt is uneven in thickness, the uneven rotation of the belt occurs and the transfer position of each color is shifted, making it difficult to manufacture the electrophotographic belt. I'm making things.

  Even in the case of a monochrome image forming apparatus, a transfer conveyance belt may be used in order to improve the printing speed and at the same time obtain an excellent image quality. This is because the transfer / conveying belt can adsorb and support the transfer material in advance and supply it to the image transfer site, so that the transfer state is stabilized and the effect of preventing the transfer material from being wound around the electrophotographic photosensitive member can be obtained.

  When used as an intermediate transfer belt, the degree of freedom in arranging inside an image forming apparatus is increased compared to the case of using a rigid cylinder such as an intermediate transfer drum, and the apparatus body can be made smaller by effectively using space. And cost reduction.

  However, these electrophotographic belts must satisfy various characteristics depending on the purpose of use, and there are many problems to be solved. In particular, in recent years, in order to improve image quality, the exposure spot diameter and developer (toner) particle diameter have been made finer in image forming apparatus bodies such as LBPs (laser beam printers) and copiers, and development and transfer electric field control. It incorporates various means such as densification. As a result, very high-definition images have come to be obtained, but on the other hand, cost reduction is also an important issue, such as a method to reduce the number of parts and giving many functions to one part, etc. As much as possible, miniaturization and weight reduction of the device are being promoted. In addition, as the price of the main unit declines, the purchase range expands, and a design that is expected to be used in a wide range of environments with low temperature and low humidity or high temperature and high humidity compared to conventional cases such as small offices and general households has come to be required. It is coming. As a result, it is more important than ever for electrophotographic belts such as intermediate transfer belts and transfer conveyance belts to improve image quality, reduce costs, handle a wide range of environments, and optimize the design to match the configuration of the main body of the image forming apparatus. It can be said that

  The electrophotographic belt uses a means for mixing some resistance control substance to adjust the resistance. However, each means has advantages and disadvantages. For example, although particulate conductive fillers such as carbon black and conductive metal oxide particles tend to have low resistance, resistance unevenness due to non-uniform particle aggregation and dispersion tends to occur. In particular, aggregates of these conductive particles with very low resistance have a great influence on the transfer electric field at the site, causing discoloration in the form of spots in the range exceeding the size of the aggregates, or dielectric breakdown (so-called leakage phenomenon). ). In addition, when such particulate additives are added, the bending resistance of the electrophotographic belt is lowered, and there are problems such as damage during repeated use. Improvement of the means is necessary.

  Furthermore, there is a very difficult problem in the uniformity of the resistance. For example, even when a belt in which a low molecular weight ionic conductive agent is dispersed, the volume resistivity or the surface resistivity is sufficiently lowered and the resistance uniformity is increased is used as an intermediate transfer belt, there is an image problem caused by a discharge phenomenon. May occur. This phenomenon occurs when a solid or halftone image is printed in a low-temperature, low-humidity environment, causing a peeling discharge in the primary transfer section or secondary transfer section, disturbing the toner image, and causing a polka dot transfer failure. is there. On the other hand, in a high-temperature and high-humidity environment, striped density unevenness may occur in parallel with the electrophotographic photosensitive member. In high-temperature and high-humidity environments, the resistance of each part decreases and the discharge phenomenon decreases, but the charge amount of the toner also decreases.Therefore, even if it is very weak at the primary transfer part, primary transfer occurs when peeling discharge occurs. It is considered that non-uniform charges are given to the toner, and the secondary transfer efficiency is partially changed due to the variation in the charge amount, resulting in striped image unevenness. This phenomenon can be improved even if the surface resistivity and volume resistivity are the same by creating a non-uniform dispersion state of the conductive agent of several μm to several tens of μm in the electrophotographic belt with the conductive filler. From this point, it is speculated that there is a need for a microscopic point of charge release, which indicates that resistance control alone cannot solve the problem. However, since the aggregate of conductive particles causes a decrease in withstand voltage, it is very difficult to control.

  Although there is a means of mixing a fibrous additive into an electrophotographic belt as a means that has higher conductivity with respect to the granular conductive filler, can reduce the amount of addition, and can improve the bending resistance. For example, a carbon fiber obtained by cutting a carbon fiber having a diameter of about several μm to 20 μm into a length of about several tens of μm to several mm has a fiber diameter that is too large, resulting in a decrease in the withstand voltage of the belt and uneven resistance. Increasing the thickness of the belt in order to avoid a decrease in the withstand voltage is not preferable because this causes a vicious circle in which the uneven thickness of the electrophotographic belt is deteriorated and the color shift is deteriorated. On the other hand, Japanese Patent Application Laid-Open No. 2002-214928 related to Patent Document 1 proposes an endless belt including carbon fibrils having a fiber diameter of 100 nm or less and an aspect ratio of 5 or more. Such fine carbon fibrils are effective in terms of high conductivity compared to granular carbon black and the above carbon fibers, but on the other hand, they are insufficient for the above-mentioned suppression of the discharge phenomenon and control of the dispersion state. . Although the cause is not clear, the optimal discharge point cannot be obtained due to the too small particle size, and the atomic arrangement is smooth, so it is expected that the layer separation will occur at the interface with the binder, resulting in poor dispersion and uneven resistance . Furthermore, since the resistance of the belt changes greatly even with a slight difference in the amount of carbon fibril added, there is a problem that it is difficult to control the resistance required for the electrophotographic belt.

  In the case of the transfer / conveying belt, paper enters between the belt and the photosensitive member, and thus, although not as noticeable as the intermediate transfer belt, there is a similar tendency, which must be solved.

  The adjustment of the electrical characteristics of the electrophotographic belt has become a more complicated factor in order to reduce the cost of the main unit, such as omitting the separation charger and pre-secondary charger, and reducing the number of power supply units. It is mentioned that an electrophotographic belt having excellent performance is required. There is an increasing number of non-magnetic one-component development methods that can be made smaller than the two-component development method, but this method is disadvantageous compared to two-component development using a carrier in that it provides a uniform and high charge amount to the toner. In some cases, the toner charge amount decreases when the development conditions are severe, such as in a high-temperature and high-humidity environment, and the transferability may decrease. In addition, as a result of the progress of uniform development as another factor, it is presumed that the non-conspicuous level of transfer non-uniformity has become apparent. In addition to these, the expansion of the use environment further increases the discharge phenomenon and density unevenness, making it more difficult to design an electrophotographic belt.

Further, the cleaning mechanism for the toner remaining on the electrophotographic belt applies a charge having a polarity opposite to that of the primary transfer to the transfer residual toner by the charging device, and returns to the electrophotographic photoreceptor simultaneously with the primary transfer. A method of collecting with a cleaning mechanism is preferred. According to this method, the number of waste toner boxes can be reduced or the waste toner transport mechanism compared to the case where a cleaning device such as a fur brush or blade is provided on the electrophotographic belt to perform cleaning separately from the electrophotographic photosensitive member. Therefore, it is possible to reduce the size and cost of the apparatus body. In this case, since it is not necessary to replace a plurality of waste toner boxes, the maintainability is improved. However, if a uniform and appropriate charge is not applied to the residual toner on the intermediate transfer belt, cleaning failure or interference with the primary transfer toner will occur, resulting in image problems. Therefore, the intermediate transfer belt and the conductive roller or corona It is necessary that a uniform current flows between cleaning charging mechanisms such as a charger. Accordingly, the uniformity of the resistance and discharge phenomenon of the intermediate transfer belt is an essential element for simultaneous transfer cleaning.
Japanese Patent Laid-Open No. 2002-214928

  As described above, an image forming apparatus and an electrophotographic belt that have solved various problems in an image forming apparatus using an electrophotographic belt have not yet been obtained.

  The object of the present invention is to obtain high image quality without image problems or scattering related to fine discharge phenomenon such as polka dot image omission or stripe density unevenness, density unevenness of electrophotographic belt pitch, etc. It is an object to provide an electrophotographic belt and an image forming apparatus that can obtain a good image even if the fluctuations occur.

  The above-described problem is applied to an electrophotographic image forming apparatus in which an electrostatic latent image formed on a photoreceptor is developed with a developer, and the obtained visible image is transferred onto a transfer material by applying a voltage. An electrophotographic belt comprising at least a thermoplastic resin and a conductive agent, the conductive agent being a fine fiber mainly composed of carbon, having an average diameter of 0.1 μm to 1 μm, an average length of 1 μm or more and This can be solved by having a characteristic that the average diameter is 10 times or more.

  The above-described problem is applied to an electrophotographic image forming apparatus in which an electrostatic latent image formed on a photoreceptor is developed with a developer, and the obtained visible image is transferred onto a transfer material by applying a voltage. An electrophotographic belt comprising at least a thermoplastic resin and a conductive agent, wherein the conductive agent is mainly composed of carbon, and is apparently formed by superimposing minimum structural units having cylindrical shapes having different average diameters at both ends. Furthermore, it can be solved by using a conductive agent having an average diameter of 0.001 μm to 1 μm in a fibrous form, an apparent average length of 0.5 μm or more, and a length of 10 times or more with respect to the average diameter.

  In the electrophotographic image forming apparatus in which the electrostatic latent image formed on the photosensitive member is developed with a developer and the obtained visible image is transferred onto a transfer material by applying a voltage. This can be solved by using the electrophotographic belt described above in the image forming apparatus.

  In order to solve various problems in the present invention, there is a great feature in the size or shape of the conductive agent used. The conductive agent mainly composed of carbon of the present invention can adjust the resistance with a relatively small addition amount, and at the same time has a large length with respect to the thickness. And the effect of suppressing image defects due to a decrease in withstand voltage or a discharge phenomenon is high. In the present invention, when the average diameter of the conductive agent is less than 0.1 μm, image defects due to fine discharge are likely to occur, and poor dispersion occurs. When the average diameter exceeds 1 μm, the withstand voltage is lowered and dielectric breakdown occurs. The average diameter is preferably 0.1 μm to 0.5 μm. Further, the average length must be 1 μm or more and 10 times or more the average diameter. If it is smaller than this range, the conductivity is lowered, and the elastic modulus and the bending resistance of the electrophotographic belt are lowered. A preferred range is 10 to 30 times. The average length is preferably 30 μm or less. If it is too long, the withstand voltage may be lowered. In addition, as shown schematically in FIG. 7, it is hollow and has a small φr2 with respect to φr1 and a cylindrical shape with different average diameters at both ends. An upper fiber structure is preferable. According to this shape, good characteristics can be obtained when the average diameter is in the range of 0.001 μm to 1 μm. The point that graphite is not a carbon fibril in the form of a hollow fiber as described in JP-A-2002-214928 is important for achieving the effect.

  At first glance, it looks like a continuous fiber, but the smallest structural unit is much smaller, and there are irregularities and voids at the atomic or molecular level on the surface and on the surface. Good and layer separation hardly occurs. In addition, the large number of such voids and irregularities is effective in stably controlling the effect of suppressing image defects and the resistance caused by the above-described discharge phenomenon. Although this factor is not certain, it is expected that the movement of electrons due to the tunnel effect is larger than that of the protrusion, and excessive charge accumulation does not occur. In addition, the graphite fiber has a smooth electron flow and a high resistance reduction effect. However, the resistance fluctuation due to the added amount abruptly occurs and is difficult to control, whereas the material of the present invention also controls the resistance. easy. Such a shape can be observed with a transmission electron microscope (TEM). In the present invention, the conductive agent made of carbon as shown in FIG. 8 is partly separated or cut when the resin is melt-kneaded. Since the above-mentioned carbon fibrils have very strong bonds between carbon atoms and no cutting occurs first, it is clear from this that the material of the present invention is different from the above-mentioned carbon fibrils. Thus, a small amount of fine particles separated during melt-kneading is considered to be one of the factors that effectively work against image defects due to resistance and discharge phenomenon. Because it is not a monolithic fiber even though it is continuous in a fibrous form, it has higher conductivity control and discharge suppression effects than fine carbon fibrils with an average diameter of 0.01 μm or less, and is more conductive than particulate carbon black. It is possible to reduce the amount of addition, and it is characterized in that the effect of improving the bending resistance of the belt and reducing defects due to the aggregation of particles can be obtained. In the case of having this structure, good conductivity can be obtained with an average length of 0.5 μm or more. The average length is preferably 30 μm or less, and the average length is preferably in the range of 30 to 5000 times the diameter.

  According to the present invention, it is possible to provide an electrophotographic belt capable of obtaining a high image quality without polka dot transfer omissions or striped uneven scattering in a wide range of environments, and an image forming apparatus including the electrophotographic belt. It becomes.

  The best mode for carrying out the present invention will be described in detail below.

  Examples of materials, manufacturing methods, and forms for carrying out the present invention are shown, but are not necessarily limited to the following.

  The thermoplastic resin, which is the main material among the molding raw materials used for the belt of the present invention, is not particularly limited as long as it satisfies the characteristics of the present invention. For example, olefinic resins such as polyethylene and polypropylene, polystyrene resins, acrylic resins, polyester resins, polycarbonate resins, polyamide resins, modified polyphenylene oxide resins, polyacetal resins, and also sulfur-containing materials such as polysulfone, polyethersulfone and polyphenylene sulfide. Resins, fluorine-containing resins such as polyvinylidene fluoride and polyethylene-tetrafluoroethylene copolymer, polyurethane resins, silicone resins, ketone resins, polyvinylidene chloride, thermoplastic polyimide, various thermoplastic elastomers, and various modified resins One type or two or more types of copolymers can be used.

  Subsequently, the conductive agent is a feature of the present invention, and among the fibrous form mainly composed of graphite or the apparently fibrous form having the structure of FIG. A method for obtaining such a hollow fibrous material composed of fine carbon has been known for a long time. Production methods are generally those in which carbon is grown in the gas phase, and there are various methods such as CVD methods and laser evaporation methods using arc discharge. Well, not particularly restricted.

  In the electrophotographic belt of the present invention, another conductive agent may be used in combination as necessary, but care must be taken with respect to the amount used and addition means in order to suppress deterioration of characteristics. For example, conductive antistatic agents such as carbon black, conductive metal oxide particles and metal powders, solid electrolytes such as surfactants, organic salts and inorganic salts, and glycols and polyethers. And so-called ionic conductive agents. However, it is preferable to select a material that is sufficiently compatible with the main thermoplastic resin and does not cause bleeding. Furthermore, there are means such as selecting a material having low resistance for the thermoplastic resin or thermoplastic elastomer as the main binder. In addition, if necessary, it is necessary to add other materials such as lubricants, non-conductive metal oxide particles, various pigments, etc., if it is necessary to improve the releasability, strength, or color of the belt for electrophotography. Also good. Examples of the lubricant include fine powder of PTFE and silicone resin, and examples of the reinforcing material include silicon dioxide, titanium dioxide, zinc oxide, calcium carbonate, and aluminum oxide.

  An example of the embodiment of the present invention is shown below.

  The molding method is preferably a production method that can produce a seamless belt, has high production efficiency, and can reduce costs. As a means for this, there is a method of producing a belt by continuously melting and extruding from an annular die and then cutting to a required length. For example, tube extrusion or inflation molding is suitable. Inflation molding not only has high molding efficiency, but also has the advantage that it is possible to extrude a plurality of sizes of tubes with different diameters from one type of die, reducing capital investment when deploying to multiple models. Furthermore, since it is expanded in a molten state at the time of extrusion, there is an advantage that a portion thicker than normal extrusion is selectively stretched in the circumferential direction and thickness unevenness is reduced. As another manufacturing means, there is a manufacturing method in which a sheet is formed by a T-die, cut to a desired length, end portions are joined, and a belt is formed. This method has advantages such as high uniformity of film thickness and the ability to improve the mechanical strength of the film because a biaxial stretching apparatus can be used. However, on the other hand, in order to avoid the seam, there is a problem that the design of the image forming apparatus main body is affected.

  The thickness of the electrophotographic belt in the present invention is preferably in the range of 40 μm to 300 μm, particularly 50 μm to 200 μm. By setting it within this range, the molding stability becomes good, thickness unevenness hardly occurs, the durability strength is sufficient, and it is possible to effectively prevent the belt from breaking or cracking. In addition, the increase in cost due to the increase in material can be suppressed, and the difference in peripheral speed between the inner surface and outer surface of the tensioning shaft when incorporated in the image forming apparatus main body increases. The occurrence of image splattering due to the shrinkage of the image can be effectively suppressed. Furthermore, the bending durability is lowered and the belt rigidity becomes too high, so that the driving torque is increased, and the main body is not enlarged and the cost is not increased. In addition, the thickness accuracy is affected by the distance between transfer stations for each color of the image forming apparatus, so it cannot be generally stated, but generally the thickness unevenness (difference between the average value and the maximum or minimum value) is ± 10 μm. Preferably, it is ± 5 μm or less. At the same time, in order to suppress color misregistration, the elastic modulus of the electrophotographic belt is preferably high, and is preferably 500 MPa or more.

  FIG. 5 shows an example of a molding apparatus according to the present invention. The apparatus basically comprises an extruder, an extrusion die, and a gas blowing device.

  First, a molding resin, a conductive agent, an additive, and the like are premixed in advance based on a desired formulation, and then the kneaded and dispersed molding raw material is charged into a hopper 102 provided in the extruder 100. In the extruder 100, the set temperature and the screw configuration of the extruder are selected so that the forming raw material has a melt viscosity that enables belt forming in a subsequent process, and the raw materials are uniformly dispersed. The forming raw material is melted and kneaded in the extruder 100 to become a melt and enters the annular die 103. The annular die 103 is provided with a gas introduction path 104. When air is blown from the gas introduction path 104 into the center of the annular die 103, the melt that has passed through the die 103 expands and expands in the radial direction, thereby forming a cylindrical shape. Film 110 is obtained. The gas blown at this time can select nitrogen, a carbon dioxide, argon, etc. other than air. The expanded molded body is pulled upward while being cooled by the external cooling ring 105. Usually, in the inflation apparatus, the tube is crushed from the left and right with the stabilizing plate 106, folded into a sheet shape, pinched by the pinch roller 107 so that the air inside does not escape, and taken at a constant speed. Next, the taken film is cut by the cutting device 108 to obtain a tubular film having a desired size.

  In the present invention, the number of layers may be increased. However, the elastic modulus of the electrophotographic belt is preferably 500 MPa or more regardless of the number of layers. In addition, an electrophotographic belt made of only an elastic material is not preferable because color shift occurs.

  This may be repeated with materials having different compositions, and two or more types of cylindrical films may be formed and laminated using an adhesive, or may be multilayered by means of welding with heat or a solvent. Simultaneous extrusion of two layers is also possible. In that case, as shown in FIG. 6, an extruder 101 is additionally arranged, and the two-layer annular die 103 is extruded simultaneously with the kneaded melt of the extruder 100. A two-layer belt can be obtained by feeding the kneaded melt of the machine 110 and expanding and expanding two layers simultaneously. Of course, when there are three or more layers, an extruder may be prepared corresponding to the number of layers. As described above, in the present invention, not only a single layer but also a multilayer electrophotographic belt can be formed in a single step and with high dimensional accuracy in a short time. The fact that this short-time molding is possible sufficiently suggests that mass production and low-cost production are possible.

  When inflation molding is performed in the present invention, the former is a comparison of the thickness ratio of the molded cylindrical film to the thickness ratio of the annular die and the molded cylindrical film, that is, the width of the gap (slit) of the annular die. On the other hand, the latter is preferably 1/3 or less, and more preferably 1/5 or less. Similarly, when the ratio of the diameter of the annular die to the outer diameter of the die slit of the annular die 103 is expressed as a percentage of the outer diameter of the cylindrical film 110, it is 50% to 400%. A range is preferred. These represent the stretched state of the material, and when the thickness ratio is greater than 1/3, the stretching is insufficient, and problems such as a decrease in strength and unevenness in resistance and thickness may occur. On the other hand, when the outer shape exceeds 400% or less than 50%, the film is stretched excessively, the molding stability is lowered, and it is difficult to secure the necessary thickness in the present invention.

  Next, the cylindrical film may be processed using a mold for the purpose of adjusting the surface roughness and dimensions, or removing the crease attached to the film during molding. Specifically, there is a method of using a set of cylindrical shapes having different diameters made of materials having different linear expansion coefficients. The material is selected so that the linear expansion coefficient of the small-diameter cylindrical (inner mold) is larger than that of the large-diameter cylindrical (outer mold). For example, the inner mold is made of aluminum, and the outer mold is made of stainless steel. After covering the inner mold with the cylindrical film, the inner mold is inserted into the outer mold, and the cylindrical film is sandwiched between the inner mold and the outer mold. At this time, it is preferable that the inner mold is designed to be slightly larger than the cylindrical film and the film is covered while being stretched. The gap between the molds is obtained by calculating the difference between the heating temperature and the linear expansion coefficient between the inner and outer molds and the required pressure. Here, the mold set in the order of the inner mold, the cylindrical film, and the outer mold is heated to near the softening point temperature of the resin. By heating, the inner mold having a large linear expansion coefficient expands from the outer mold, and a uniform pressure is applied to the entire surface of the cylindrical film. At this time, since the surface of the resin film that has reached the vicinity of the softening point is pressed against the inner surface of the outer mold and the back surface is pressed against the inner mold surface, each surface roughness can be individually controlled. Then, the desired surface property can be obtained by cooling and removing the film from the mold. For example, the surface of the electrophotographic belt is mirrored to increase the charging potential, and the back surface has a certain degree of roughness so that the charging potential can be lowered. Moreover, the removal of a crease | fold and fine adjustment of a dimension can be performed also by the method of covering and heating the film shape | molded using only said inner type | mold.

  Thereafter, if necessary, the reinforcing member, the guide member, and the position detecting member are attached or precision cut to manufacture an electrophotographic belt. Moreover, although the method of disperse | distributing a material can use a normal method, since the means to melt-extrude with a biaxial extruder can obtain high shearing force (share), it is suitable for uniform dispersion | distribution of material. In particular, care must be taken when dispersing the conductive agent of the present invention. Therefore, not only melt-kneading with a twin screw extruder, but also a means of previously melting and kneading a high-concentration material with a kneader or the like and a method of treating the conductive agent with various coupling materials, When powder resin is used, it is easy to mix with conductive particles by premixing, and various means are used singly or in combination, such as powder resin dissolves quickly during melt extrusion, making it difficult to form aggregates of conductive particles. It is preferable.

  In order to further enhance the effects of the present invention, the average circularity of the circularity frequency distribution of the toner is preferably 0.920 to 0.995, more preferably 0.950 to 0.995, and still more preferably 0.970 to 0.970. 0.990 is preferable. Since such toner has high transfer efficiency, it can be used in combination with the electrophotographic belt of the present invention, and has the effect of improving high-temperature and high-humidity striped image defects that occur particularly when transferability is lowered. Become very large. Further, when the circularity standard deviation of the circularity frequency distribution of the toner particles is preferably less than 0.040, more preferably less than 0.035, and even more preferably 0.015 or more and less than 0.030, the charge uniformity of the toner is further improved. improves. Further, the circle equivalent number average diameter D1 (μm) is preferably in the range of 2 to 10 μm.

  The circularity in the present invention is an index indicating the degree of unevenness of the toner, and is 1.000 when the toner is a perfect sphere. The more complicated the surface shape, the smaller the circularity.

  Next, an example of an image forming apparatus using the belt of the present invention is shown.

  FIG. 1 shows a full-color image forming apparatus (copier or laser beam printer) using an electrophotographic process.

  A rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 that is repeatedly used as a first image bearing member is rotationally driven in a direction indicated by an arrow with a predetermined peripheral speed (process speed).

  The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the primary charger 2 during the rotation process. Reference numeral 32 denotes a power source for the primary charger. Here, alternating current is superimposed on direct current, but only direct current may be applied. Next, by unshown exposure means (color separation / imaging exposure optical system of full-color original image, scanning exposure system by laser scanner that outputs laser beam modulated in accordance with time series electric digital pixel signal of image information, etc.) By receiving the exposure light 3, an electrostatic latent image corresponding to a first color component image (for example, a yellow color component image) of the target full-color image is formed. Next, the electrostatic latent image is developed with yellow toner Y as the first color by the first developing device (yellow color developing device 41). At this time, the developing units of the second to fourth developing units (magenta color developing unit 42, cyan color developing unit 43, and black color developing unit 44) are turned off and do not act on the photosensitive drum 1. The first color yellow toner image is not affected by the second to fourth developing units.

  The intermediate transfer belt 5 is rotationally driven at the same peripheral speed as the photosensitive drum 1 in the direction of the arrow. The yellow toner image of the first color formed and supported on the photosensitive drum 1 is applied from the primary transfer roller 6 to the intermediate transfer belt 5 in the process of passing through the nip portion between the photosensitive drum 1 and the intermediate transfer belt 5. The primary transfer is sequentially performed on the outer peripheral surface of the intermediate transfer belt 5 by an electric field formed by the primary transfer bias. The surface of the photosensitive drum 1 after the transfer of the first color yellow toner image corresponding to the intermediate transfer belt 5 is cleaned by the cleaning device 13. In the same manner, the second color magenta toner image, the third color cyan toner image, and the fourth color black toner image are sequentially superimposed and transferred onto the intermediate transfer belt 5 and synthesized corresponding to the target full color image. A color toner image is formed. The secondary transfer roller 7 is disposed in parallel with the secondary transfer counter roller 8 so as to be separated from the lower surface of the intermediate transfer belt 5 by bearing in parallel. A primary transfer bias for sequentially superimposing and transferring the first to fourth color toner images from the photosensitive drum 1 to the intermediate transfer belt 5 is applied from a bias power source 30 with a polarity (+) opposite to that of the toner. The applied voltage is, for example, in the range of +100 V to 2 kV. In the primary transfer step of the first to third color toner images from the photosensitive drum 1 to the intermediate transfer belt 5, the secondary transfer roller 7 can be separated from the intermediate transfer belt 5. In transferring the composite color toner image transferred onto the intermediate transfer belt 5 to the transfer material P, the secondary transfer roller 7 is brought into contact with the intermediate transfer belt 5 and the transfer material guide 10 is moved from the paper feed roller 11. Then, the transfer material P is fed to the contact nip between the intermediate transfer belt 5 and the secondary transfer roller 7 at a predetermined timing, and a secondary transfer bias is applied from the power source 31 to the secondary transfer roller 7. By this secondary transfer bias, the composite color toner image is secondarily transferred from the intermediate transfer belt 5 to the transfer material P as the second image carrier. At this time, an apparatus for assisting charging of the toner image before the secondary transfer on the intermediate transfer belt is not added to the apparatus. The transfer material P that has received the transfer of the toner image is introduced into the fixing device 15 and heated and fixed. After the image transfer to the transfer material P is completed, a cleaning charging member 9 disposed so as to be detachable is brought into contact with the intermediate transfer belt 5, and a transfer material having a polarity opposite to that of the photosensitive drum 1 is applied. The transfer residual toner that is not transferred to P but remains on the intermediate transfer belt 5 is given a charge having a polarity opposite to that at the time of primary transfer. Reference numeral 33 denotes a bias power source. Here, an alternating current is superimposed on a direct current and applied. The transfer residual toner charged to a polarity opposite to that at the time of primary transfer is electrostatically transferred to the photosensitive drum 1 at and near the nip portion with the photosensitive drum 1, thereby cleaning the intermediate transfer member. Since this step can be performed simultaneously with the primary transfer, the throughput does not decrease.

  Next, a process cartridge in which the intermediate transfer belt and the electrophotographic photosensitive member are integrally supported will be described with reference to FIG. The process cartridge only needs to be configured so that at least the intermediate transfer belt 5, the electrophotographic photosensitive member 1, and the primary transfer means 6 are integrally supported and are detachable from the apparatus main body. In FIG. 2, an intermediate transfer belt cleaning mechanism 13 and an electrophotographic photosensitive member cleaning mechanism 9 are also attached as an integrated unit. As described above, the cleaning of the intermediate transfer belt of the present invention is a mechanism necessary for charging the transfer residual toner to a polarity opposite to that of the primary transfer and returning it to the electrophotographic photosensitive member at the primary transfer portion. Equipped with a body-cleaning roller 9. Cleaning of the electrophotographic photosensitive member is blade cleaning. In this cartridge, a waste toner container is also integrated, and the transfer residual toner on both the intermediate transfer belt and the electrophotographic photosensitive member is discarded at the same time when the cartridge is replaced, which contributes to improvement in maintainability. Further, the intermediate transfer belt is stretched by two rollers of a driving roller 8 and a tension roller 12 to reduce the number of parts and reduce the size. Here, the driving roller 8 is simultaneously a counter roller of the cleaning roller. The tension roller 12 that rotates following the intermediate transfer belt has a sliding mechanism, is pressed in the direction of the arrow by a compression spring, and applies tension to the intermediate transfer belt. The slide width is about 1 to 5 mm, and the total pressure of the spring is about 5 to 100N. The electrophotographic photosensitive member 1 and the driving roller 8 have a coupling (not shown) so that a rotational driving force is transmitted from the main body.

  Further, another example of the image forming apparatus is shown in FIGS. 3 and 4 are provided with the same number of developers as the number of developers necessary for image formation, and there is an advantage that the printing speed of full-color printing is remarkably improved.

  FIG. 3 uses an intermediate transfer belt. Similar to 1, the visible image formed on the electrophotographic photosensitive member 1 is sequentially transferred to the intermediate transfer belt 5 and superimposed, and then the toner is transferred to the toner by the secondary transfer roller 7. A reverse polarity bias is applied, and the transfer is performed on the transfer material P at once. The developer remaining on the intermediate transfer belt is removed by the cleaning device 18.

  FIG. 4 shows an example of the transfer conveyance belt system. The transfer material P is biased by the suction roller 63 and is sucked and transported to the transfer transport belt 16. The image of each color formed on the electrophotographic photosensitive member is sequentially transferred to the transfer material P adsorbed on the transfer conveyance belt by applying a bias having a polarity opposite to that of the toner from the transfer roller 17 and superimposed, and then fixed. Heat fixing is performed by the device 15.

  Next, a method for measuring each characteristic in the present invention will be described.

<Elastic modulus measurement method>
A sample is cut out from the belt for electrophotography with a width of 20 mm and a length of 100 mm in the circumferential direction, and after measuring the thickness, the sample is mounted on a tensile tester (Tensilon RTC-1250A, manufactured by Orientec Corp.). The thickness is the average of 5 points in the sample. Conduct a tensile test with a measurement interval of 50 mm and a test speed of 5 mm / min, record the elongation and stress with a recorder, read the stress when the elongation is 0.2% and 0.5%, and calculate the elastic modulus using the following formula: calculate.

  This measurement is performed 5 times, and the average value is the elastic modulus of the present invention.

Elastic modulus = (f2−f1) / (20 × t) × 1000 [MPa]
(In the formula, f1 represents a stress [N] of 0.2% elongation, f2 represents a stress [N] of 0.5% elongation, and t represents a thickness [mm] of the sample.)

<Electrophotographic belt thickness measurement method>
Measurements were made at intervals of 10 mm in the circumferential direction of the electrophotographic belt using a dial gauge having a minimum memory of 1 μm, and an average value, a maximum value, and a minimum value were obtained. The thickness unevenness was defined as a difference between the maximum value and the minimum value with respect to the average value.

<Measurement method of conductive material size>
The conductive agent was observed with SEM (scanning electron microscope) or TEM (transmission electron microscope), the length was measured for any 20 individuals, and the diameter was measured and averaged at three locations for each individual. The measurement magnification was appropriately adjusted according to the size of the conductive agent, and the conductive agent was dispersed in the embedding agent as necessary, and observation was performed by slicing with a microtome.

<Toner circularity measurement method>
In the present invention, the equivalent circle diameter, circularity, and frequency distribution of the toner are used as a simple method for quantitatively expressing the shape of the toner particles. In the present invention, the flow type particle image measuring device “FPIA” is used. -1000 "(manufactured by Toa Medical Electronics Co., Ltd.) was used for measurement, and calculation was performed using the formula 1 described later.

  Here, the “particle projected area” is the area of the binarized toner particle image, and the “peripheral length of the particle projected image” is the length of the contour line obtained by connecting the edge points of the toner particle image. Define. The circularity in the present invention is an index indicating the degree of unevenness of the toner, and is 1.000 when the toner is a perfect sphere. The more complicated the surface shape, the smaller the circularity. In the present invention, the circle-equivalent number average diameter D1 (μm) and the particle diameter standard deviation SDd, which mean the average value of the particle number frequency distribution based on the number of toners, are the particle diameter (center value) at the dividing point i of the particle size distribution. Is di and frequency is fi.

Hereinafter, the present invention will be described in more detail with specific examples. In the examples,% means mass%.
(Type of conductive agent)
Conductive agent A
An apparently hollow carbon fiber having an average length of 6.8 μm and an average diameter of 0.011 μm having the structure of FIG. 8 obtained by vapor growth of carbon.
Conductive agent B
An apparently hollow carbon fiber having a structure similar to that of the conductive agent A, an average length of 3.8 μm, and an average diameter of 0.008 μm.
Conductive agent C
Hollow carbon fiber having an average diameter of 0.15 μm and an average length of 15.6 μm (not having the structure of FIG. 8)
Conductive agent D
Carbon fiber having an average diameter of 0.81 μm and an average length of 22.6 μm (not having the structure of FIG. 8)
Electrophotographic belt molding compound 1
PBT (polybutylene terephthalate) 70%
Conductive agent A 30%
The above material is stirred while being heated with a pressure kneader, and the conductive agent is sufficiently dispersed in the PBT, then taken out from the kneader, roughly cut with a cutter, and further pulverized to obtain a master batch 1 having a diameter of 2 to 3 mm. It was.
The master batch 1 and PBT were mixed at the following ratio using a biaxial extruder, extruded with a strand and cut to obtain a compound 1 for forming an electrophotographic belt.

PBT (polybutylene terephthalate) 90.5%
Masterbatch 1 9.5%
Belt molding compounds 2 to 6 were produced in the same manner as belt molding compound 1 except that the blending amounts and materials were changed as shown below.
Electrophotographic belt molding compound 2
Masterbatch 2
80% PBT (polybutylene terephthalate)
Conductive agent B 20%
The said masterbatch 2 was mixed in the following ratio using the following biaxial extruder, and it was set as the pellet.

PBT (polybutylene terephthalate) 91%
Masterbatch 2 9%
Electrophotographic belt molding compound 3
Masterbatch 3
PA (polyamide) 70%
Conductive agent C 30%
The master batch 3 was mixed at the following ratio using the following biaxial extruder to obtain pellets.

PA (polyamide) 70%
Masterbatch 3 30%
Electrophotographic belt molding compound 4
Master batch 4
PA (polyamide) 70%
Conductive agent D 30%
The master batch 3 was mixed at the following ratio using the following biaxial extruder to obtain pellets.

PA (polyamide) 60%
Masterbatch 4 40%
The following electrophotographic belt was formed using the above compound, and a print test was conducted.

  Molding was performed using the molding apparatus of FIG. In FIG. 5, the molding die 103 was an annular die, and an annular slit having an outer diameter of φ100 mm was used. The die slit was 1.0 mm. In this molding apparatus, the belt molding compound 1 sufficiently heated and dried was put into the material hopper 102 of the extruder, heated and melted, and extruded from the annular die in a cylindrical shape. At this time, an external cooling ring 105 was installed around the die, and cooling was performed by blowing air from the periphery to the extruded film. Subsequently, air was blown into the extruded tubular film through the gas introduction passage 104, and the air was expanded to a diameter of 139 mm, and then continuously taken out at a constant speed by a take-up device. The cylindrical film was cut with a cutting device 108 following the pinch roller. The cylindrical film was adjusted in size and surface smoothness using a pair of cylindrical molds made of metals having different linear expansion coefficients, and creases were removed at the same time. First, the tubular film 1 manufactured with a diameter of 139 mm was covered with an inner mold made of aluminum with a diameter of 140 mm while slightly extending. Subsequently, the inner mold was inserted into a stainless outer mold whose inner surface was processed into a mirror surface, and heated to a temperature at which the resin melted. As the temperature rose, the inner mold with a large linear expansion coefficient pressed the tubular film 1 against the outer mold, and the surface roughness and dimensions of the back and front were adjusted. The temperature was raised for 1 minute to cool. After cooling, the end portion was precisely cut so as to have a width of 250 mm after being removed from the mold, and rubber meandering preventing members were attached to the back surfaces of both end portions of the belt to produce an electrophotographic belt 1 having a diameter of 140 mm. The electrophotographic belt 1 had an elastic modulus of 1380 [MPa], an average thickness of 110 μm, and thickness unevenness within ± 5 μm.

<Print test>
The electrophotographic belt 1 having a diameter of 140 mm was attached to one image forming apparatus. The toner has a particle size of 6.5 μm, a circularity of 0.981, a circularity standard deviation of 0.021, and a toner having a circularity of less than 0.95 produced by a suspension polymerization method having 2.6% by number of toner particles. The developing method used was a non-magnetic one-component method. The process speed was 120 mm, the intermediate transfer belt and the photosensitive member were individually driven, and the speed of the intermediate transfer belt was set to 100.3 with respect to the speed 100 of the photosensitive member. An A4 size full color image print confirmation test was performed at a speed of 4 sheets per minute in an environment of 23 ° C./55% RH. As a result, there were no particularly problematic images such as image density unevenness or partial transfer omission, and the results were satisfactory. Thereafter, after a durability test of 5,000 full-color sheets was performed at a printing rate of 4%, an image was confirmed with the same pattern, but there was no particular problem and the result was satisfactory.

  Next, when a print test was conducted in the same manner in an environment of high temperature and high humidity (H / H) 30 ° C./80% RH and low temperature and low humidity (L / L) 15 ° C./10% RH, a good image with no particular problems was obtained. was gotten. In addition, (circle) evaluated that it was favorable, (triangle | delta) had no problem practically, and x was bad.

  Example 1 except that the amount of air introduced at the time of extrusion in Example 1 was adjusted, a cylindrical film having a diameter of 219 mm was formed, and the diameter of the inner mold was changed to 220 mm by changing the size of the cylindrical mold used after extrusion. In the same manner, an electrophotographic belt 2 having a diameter of 220 mm was produced. The electrophotographic belt 2 was set in the apparatus shown in FIG. 3, and a print test was conducted in the same manner as in Example 1 as a tandem intermediate transfer belt having four photoreceptors. At this time, the process speed of the intermediate transfer belt was 95 mm, and the full color printing speed was 16 sheets per minute for A4. As a result, good images could be obtained as in Example 1. The results are shown in Table 1.

  For electrophotography having a diameter of 165 mm in the same manner as in Example 1, except that the amount of air introduced during extrusion is adjusted, a cylindrical film having a diameter of 164 mm is formed, and the size of the mold is changed to 165 mm. A belt 3 was produced. The electrophotographic belt 3 was set in the apparatus shown in FIG. 4, and a print test was conducted as in Example 1 as a transfer conveyance belt. At this time, the process speed of the transfer conveyance belt is 95 mm, and the full color printing speed is 16 sheets per minute for A4. As a result, good images could be obtained as in Example 1. The results are shown in Table 1.

  The electrophotographic belt 4 was molded in the same manner as in Example 2 except that the raw material was changed to the electrophotographic belt molding compound 2 and the thickness was slightly increased, and a print test was performed. As a result, good images could be obtained as in Example 1. The results are shown in Table 1.

  The electrophotographic belt 5 was molded in the same manner as in Example 2 except that the raw material was changed to the electrophotographic belt molding compound 3 and the thickness was slightly reduced, and a print test was performed. As a result, good images could be obtained as in Example 1. The results are shown in Table 1.

  The electrophotographic belt 6 was molded in the same manner as in Example 2 except that the raw material was changed to the electrophotographic belt molding compound 4 and the thickness was slightly reduced, and a print test was performed. As a result, some image density unevenness occurred after the H / H endurance, but it was judged to be practical. The results are shown in Table 1.

[Comparative Example 1]
In Example 1, the conductive agent was changed to the following, and a comparative compound 1 was obtained by melting and kneading with a twin screw extruder, extruding with a strand, and pelletizing with a cutter, without using a masterbatch.

Comparative conductive agent 1: Diameter 3.5 μm Length 50 μm Carbon fiber blending ratio without the structure of FIG. 8 PBT (same as Example 1) 85%
Comparative conductive agent 1 15%
An electrophotographic belt was produced and tested in the same manner as in Example 1 except that the comparative compound 1 was used. As a result, partial unevenness of the image was observed from the initial stage, and an image dropout caused by defective withstand voltage occurred during the durability test. Therefore, it was judged that there was a problem in uniformity of resistance and withstand voltage.

[Comparative Example 2]
A comparative compound 2 was obtained in the same manner except that the conductive agent and the mixing ratio were changed to the following in Example 1.

Comparative conductive agent 2: A hollow carbon fiber having a diameter of 0.003 μm and a length of 5.6 μm, which does not have the structure shown in FIG.
Comparison masterbatch 1
80% PBT (polybutylene terephthalate)
Comparative conductive agent 2 20%
Comparison compound 2
90% PBT (polybutylene terephthalate)
Comparison masterbatch 1 10%
An electrophotographic belt was prepared and tested in the same manner as in Example 1 except that the comparative compound 2 was used. As a result, it was judged that the image unevenness on the stripes, which seems to be caused by the fine discharge from the beginning at H / H, was seen on the halftone, and the fine discharge suppressing effect was insufficient.

1 is a diagram showing a schematic configuration of a four-process full-color image forming apparatus using an electrophotographic belt of the present invention as an intermediate transfer belt. FIG. 2 is a diagram illustrating a schematic configuration of a process cartridge in which an intermediate transfer belt and an electrophotographic photosensitive member of the present invention are integrally supported. 1 is a diagram showing a schematic configuration of a four-conductor type full-color image forming apparatus using an electrophotographic belt of the present invention as an intermediate transfer belt. FIG. 1 is a diagram illustrating a schematic configuration of a full-color image forming apparatus using an electrophotographic belt of the present invention as a transfer conveyance belt. It is a figure which shows schematic structure of the shaping | molding apparatus of the electrophotographic belt (single layer) of this invention. It is a figure which shows schematic structure of the shaping | molding apparatus of the belt for electrophotography (2 layers) of this invention. It is a schematic diagram which shows the structural unit from which a diameter differs in the both ends of the electrically conductive agent of this invention. It is a schematic diagram which shows the structure of the overlap of the minimum structural unit of the electrically conductive agent of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Primary charger 3 Exposure light 5 Intermediate transfer belt 6 Primary transfer roller 7 Secondary transfer roller 8 Secondary transfer counter roller 9 Cleaning charging member 10 Transfer material guide 11 Paper feed roller 12 Tension roller 13 Cleaning device 15 Fixing Device 16 Transfer conveyor belt 17 Transfer roller 18 Cleaning device 30, 31, 33 Bias power source 32 Primary charger power source 41 Yellow color developing device 42 Magenta color developing device 43 Cyan color developing device 44 Black color developing device 63 Adsorption rollers 100, 101 1 Shaft extruders 102 and 109 Material hopper 103 Annular die 104 Gas introduction path 105 External cooling ring 106 Stabilizing plate 107 Pinch roller 108 Cut device 110 Cylindrical film P Transfer agent

Claims (4)

  An electrophotographic belt used in an electrophotographic image forming apparatus that develops an electrostatic latent image formed on a photoreceptor with a developer and applies a voltage to the obtained visible image on a transfer material. It contains at least a thermoplastic resin and a conductive agent, and the conductive agent is a fine fiber mainly composed of carbon, with an average diameter of 0.1 μm to 1 μm, an average length of 1 μm or more, and 10 times the diameter. An electrophotographic belt characterized by the above.   An electrophotographic belt used in an electrophotographic image forming apparatus that develops an electrostatic latent image formed on a photoreceptor with a developer and applies a voltage to the obtained visible image on a transfer material. An average containing a thermoplastic resin and a conductive agent, the conductive agent being mainly composed of carbon and having a cylindrical shape with different diameters at both ends, which are superposed on each other and apparently fibrous. An electrophotographic belt characterized by being a conductive agent having a diameter of 0.001 μm to 1 μm, an apparent average length of 0.5 μm or more and a length of 10 times or more of the diameter.   The thickness of the electrophotographic belt is 40 μm to 300 μm, the unevenness of thickness is within ± 10 μm, the elastic modulus is 500 MPa or more, and the image forming apparatus has a plurality of photoconductors. The electrophotographic belt described in 1.   An electrophotographic image forming apparatus that develops an electrostatic latent image formed on a photoreceptor with a developer, and transfers the obtained visible image onto a transfer material by applying a voltage to the image forming apparatus. An image forming apparatus using the electrophotographic belt according to claim 1.