JP2007108538A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress induced charge injection into a carrier due to a development field which acts on a development area where an image bearing member and a developer bearing member confront each other, and to form a high quality image. <P>SOLUTION: A surface of a metal sleeve 102 is coated with a resistance layer 103 the volume resistivity value of which is higher than that of a magnetic carrier 10 in a development nip part which is an area where a two-component developer 12 held by a developer bearing member 13 comes in contact with an image bearing member 14 opposite to the developer bearing member 13. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic technique for developing and visualizing an electrostatic latent image formed on an image carrier with a toner of a two-component developer held on the developer carrier. It is about.

  Conventionally, with respect to image output devices using electrophotographic technology such as laser printers and copiers, toner and developer are used to develop an electrostatic latent image formed on an image carrier and form a visible image. A two-component developer composed of a carrier and a one-component developer composed of a single toner have been used. Of these, the magnetic brush development method using a two-component developer is superior in terms of image quality compared to other development methods, can be colored, and is relatively inexpensive. Has been used.

  2. Description of the Related Art A conventional image forming apparatus using a magnetic brush developing system includes a cylindrical metal sleeve and a magnet roller in which permanent magnets, which are magnetic field generating means, are arranged alternately in N and S poles. And a developer carrying member. A two-component developer is carried on the surface of the metal sleeve of the developer carrying member, and only the metal sleeve is rotated while the magnet roller is fixed, so that the developing region facing the image carrying member on which the electrostatic latent image is formed is moved. A two-component developer can be conveyed. Then, by a developing electric field applied between the developer carrier and the image carrier, only the charged toner can be electrostatically attached to the image carrier to form a visible image.

  However, in an image forming apparatus using a conventional magnetic brush developing method, a so-called carrier adhesion occurs in which not only the toner but also the carrier adheres to the image carrier due to the developing electric field. And it is a big problem that this carrier adhesion causes an image defect. Specifically, an image defect due to white spots is caused in the image area. Further, the toner that has adhered to the carrier on the developer carrying member also adheres to the non-image area, thereby causing image fogging. Particularly in recent years, in order to meet the demand for higher image quality, the toner particle size has been reduced, and the carrier tends to have a smaller particle size. As the particle size of the carrier is reduced, the magnetic restraining force of the carrier on the developer carrying member is reduced, so that countermeasures against the carrier adhesion are increasingly required.

  Factors that control such carrier adhesion include the carrier's magnetic binding force on the developer carrier, which generally depends on the saturation magnetization of the carrier, the magnetic flux density of the magnet roller at a position facing the development area, and the toner. And charge up of the carrier due to friction with the developer carrying member. A variety of improvement measures related to control factors such as magnetic restraint force and carrier charge-up have been tried to suppress carrier adhesion.

  For example, Patent Document 1 discloses a technique of providing a roughened coating layer made of martensitic stainless steel, which is a magnetic material, on the surface of a nonmagnetic metal sleeve. According to the technique described in Patent Document 1, a part of the magnetic flux going outward from the surface of the permanent magnet member inside the developing roll passes through the coating layer and is locally guided to the convex portion of the roughened coating layer. Produces magnetic poles. For this reason, the magnetic restraining force for holding the carrier on the sleeve is increased, and carrier adhesion to the image carrier can be prevented.

  In Patent Document 2, the weight average particle diameter of the carrier, the volume resistance of the carrier, the magnetic flux density in the normal direction of the developing pole of the magnet roller, the magnetic flux density of the magnetic pole downstream of the developing pole with respect to the developing sleeve rotation direction, A technique is described in which each gap is a specified value. With this technique, it is possible to suppress carrier adhesion and obtain a high-quality image.

Patent Document 3 discloses a technique for providing a resin coating layer having a volume resistance of 10 ⁶ Ω · cm or less in which conductive particles are dispersed. By using the technique described in Patent Document 3 for the problem that the carrier adheres to the non-image area of the photosensitive member due to the triboelectric charging between the developer carrying member and the carrier, and the carrier is strongly charged to the opposite polarity to the toner, It is possible to reduce the amount of frictional charge of the carrier and reduce the carrier adhesion to the non-image area.

Further, Patent Document 4 is for suppressing fogging and a decrease in image density that occurs when the surface of the photoreceptor is a low resistance layer, and the purpose is different from the technique for suppressing carrier adhesion. A plating layer is formed on the surface of the developer carrier, and the product of the volume resistivity σ of the developer carrier and the layer thickness d of the plating layer is 1 × 10 ⁻⁶ Ω · cm ² ≦ σ × d ≦ 1 × 10 ^5. A technique of Ω · cm ² is disclosed.

In Patent Document 5, the volume resistivity of a developing sleeve having a coating layer on the sleeve base surface is set to 10 ³ Ω · cm or less, and the coating layer contains a curable resin, carbon fine particles, and titanium oxide fine particles, and is cured. A technique is disclosed in which the weight ratio of the mold resin content B to the carbon fine particle and titanium oxide fine particle content P is in the range of P: B = 1: 1.5 to 1: 3.5. With the technique described in Patent Document 5, it is possible to realize image formation with high durability, density stability, and excellent ghost stress.

Further, Patent Document 6 discloses that the amount of developer transport over time is reduced by forming a soft surface treatment layer made of a material having a material hardness lower than that of the developing sleeve in the valley of the sandblast provided on the developing sleeve surface. Techniques for preventing this are disclosed.
Japanese Patent Laid-Open No. 9-26701 (published January 28, 1997) JP 2003-323050 A (published November 14, 2003) JP 2003-5504 A (published January 8, 2003) JP 2004-37951 A (published on February 5, 2004) Patent No. 3297549 (Registered on April 12, 2002) JP 2003-330263 A (published on November 19, 2003)

  However, the carrier adhesion to the image carrier is not governed only by the magnetic restraint force and the carrier charge-up described above, and in addition to this, the induction charging of the carrier due to the effective electric field in the development region is one of the factors. ing.

  Here, the induction charging phenomenon will be described with reference to FIGS. As shown in FIG. 9A, the two-component developer 12 composed of the carrier (magnetic carrier) 10 and the toner 11 is a metal of the developer carrier 13 in which a magnet roller (not shown) is disposed in the developing region. A magnetic brush is formed on the surface of the sleeve 13 and is in contact with the image carrier 14. Here, when the DC bias voltage applied to the metal sleeve 13 is −400 V and the metal substrate of the image carrier 14 is grounded, in the image portion, the charged charge on the surface of the image carrier 14 is canceled, so the surface potential is 0V. Then, due to the electric field formed at the developing nip portion, negative induced charges are injected from the developing sleeve side into the carrier 10 at the tip of the magnetic brush. Due to this induced charge, a Coulomb force acts on the carrier 10 at the tip of the magnetic brush in the direction of moving to the image carrier 14, and when this overcomes the magnetic restraint force on the developer carrier, the carrier 10 moves to the image carrier 14. Cause carrier adhesion, and a white-out image is generated. On the other hand, in the non-image portion, as shown in FIG. 9B, the negatively charged charge on the surface of the image carrier 14 remains, and is formed at the development nip portion when the surface potential is −600V. Due to the electric field, positive induced charges are injected into the carrier 10 at the tip of the magnetic brush from the metal sleeve 13 side. As with the image portion, this induced charge causes a Coulomb force to act on the carrier 10 at the tip of the magnetic brush in the direction of moving to the image carrier 14, which overcomes the magnetic restraint force on the developer carrier. Carrier adhesion to the image carrier 14 is caused, and the toner 11 is also taken in, thereby causing image fogging.

FIG. 10 shows the development bias dependence of the number of carriers attached per A4 sheet to the image carrier. Here, the developing bias is a value represented by V _OPC -V _dev where the surface potential of the image carrier is V _OPC and the voltage applied to the developing sleeve of the developer carrier is V _dev . That is, the positive bias area indicates an image area (black solid image area), and the negative bias area indicates a non-image area (background area). In this figure, the solid line indicates the number of carriers attached only by the carrier, and the broken line indicates the number of carriers attached by the two-component developer in which the carrier and the toner are mixed. As can be seen from FIG. 10, carrier adhesion occurs in the carrier alone or in the state where the carrier and the toner are mixed. Further, since the carrier adhesion is observed in both the image area and the non-image area, it can be understood that the carrier is induction-charged in both positive and negative polarities as described above. Here, the carrier adhesion amount is decreased in the case where the carrier and the toner are mixed as compared with the case of the carrier alone, because the volume resistivity of the toner is higher than the volume resistivity of the carrier. This is because the resistance value of the developer body as a whole increases due to the mixture, and induction charging is difficult to occur.

  As described above, one cause of carrier adhesion to the image carrier is the induction charging phenomenon of the carrier due to the developing electric field. In other words, in order to reduce carrier adhesion, a system that does not easily induce induction charging is used. Need to build.

  Considering the above phenomenon, the technique of Patent Document 1 locally increases the magnetic flux density on the surface of the developing sleeve and can improve the magnetic restraining force of the carrier with respect to the developing sleeve, but it cannot prevent the induction charging phenomenon of the carrier. . For this reason, when the Coulomb force by induction charging is superior to the magnetic restraining force, carrier adhesion to the image carrier occurs. Further, the hardness of the magnetic brush is increased by increasing the magnetic binding force of the carrier. For this reason, problems such as causing streaking of the developed image and increasing the stress on the image carrier and shortening the life of the carrier and the image carrier.

  In the technique described in Patent Document 2, the magnetic binding force can be increased as in the technique of Patent Document 1, but the induction charging phenomenon cannot be prevented. For this reason, carrier adhesion is induced, and a streak streak with respect to the developed image and shortening of the life of the carrier and the image carrier are caused.

  In the technique of Patent Document 3, carrier adhesion due to charge-up of carriers can be prevented by providing a low resistance coating layer on the surface of the developing sleeve. However, since the resistance is low, the injection of induced charges into the carrier cannot be prevented, leading to carrier adhesion.

In the technique of Patent Document 4, the product of the volume resistivity σ of the developer carrier and the layer thickness d of the plating layer is 1 × 10 ⁻⁶ Ω · cm ² ≦ σ × d ≦ 1 × 10 ⁵ Ω · Although cm ^2, and the range of the volume resistivity sigma derived from the plating layer thickness 1~25μm according to the dependent ^{claims, 4 × 10 -4 Ω · cm} ≦ σ ≦ 1 × 10 9 Ω · cm and a low resistance Inductive charges easily flow into the carrier through the plating layer, and there is a concern that carrier adhesion occurs.

  Further, the techniques of Patent Documents 5 and 6 cannot prevent the induction charging phenomenon of carriers.

  The present invention has been made in view of the above-described problems, and its purpose is to induce inductive charge injection into a carrier due to a developing electric field acting on a developing region where an image carrier and a developer carrier face each other. An object is to realize an image forming apparatus that can be suppressed. Furthermore, by suppressing inductive charge injection to the carrier, carrier adhesion to the image carrier is reduced, and image omission and image are eliminated without inducing streaking of developed images and shortening of the life of the carrier or image carrier. An object of the present invention is to realize an image forming apparatus capable of forming an extremely high quality image without fog.

  In order to solve the above problems, an image forming apparatus according to the present invention has a magnetic carrier and a non-magnetic toner on the surface of a developer carrying member having a magnetic non-magnetic sleeve disposed therein and having a rotatable non-magnetic sleeve. In the image forming apparatus for developing an electrostatic latent image formed on the surface of the image carrier by the developer, the sleeve surface is held by the developer carrier. There is provided a resistance layer having a volume resistance value larger than the volume resistance value of the magnetic carrier at the developing nip portion where the developer is in contact with the image carrier facing the developer carrier. It is characterized by being.

  According to the above configuration, by providing the resistance layer having a volume resistance value larger than the volume resistance value of the magnetic carrier at the development nip portion on the surface of the sleeve of the developer carrier, the image carrier and the developer carrier Can prevent inductive charging from occurring in the opposite development areas. Therefore, it is possible to suppress inductive charge injection from the developer carrier to the magnetic carrier due to the development electric field acting on the development area where the image carrier and the developer carrier face each other. Since inductive charge injection to the magnetic carrier can be suppressed, carrier adhesion to the image carrier can be reduced. Since carrier adhesion can be reduced, it is possible to form an extremely high-quality image free from image omission and image fogging. In addition, since the magnetic restraint force is not increased as in the prior art, it is possible to form a high-quality image without inducing a sweeping streak on the developed image and shortening the life of the carrier or the image carrier. it can.

In the image forming apparatus according to the present invention, in addition to the above configuration, the magnetic carrier has a volume resistivity of 2 obtained from a dynamic resistance value measured under application of a DC voltage of 100 V at the development nip portion. .2 × 10 ¹⁰ Ω · cm or more is preferable.

According to the above configuration, by using a carrier having a volume resistivity of 2.2 × 10 ¹⁰ Ω · cm or more, injection of induced charges from the developer carrier can be reliably suppressed. Therefore, carrier adhesion to the image carrier can be further reduced, and a higher quality image can be formed.

  In the image forming apparatus according to the present invention, in addition to the above configuration, the magnetic carrier may be subjected to antistatic processing.

  According to the above configuration, since the antistatic processing is performed on the magnetic carrier, the charge up of the magnetic carrier can be suppressed. Therefore, carrier adhesion to the image carrier can be further reduced.

  In addition, as an antistatic process in the magnetic carrier, a coating layer in which a surfactant having an antistatic effect is dispersed on the surface of the magnetic carrier may be formed. In this case, the surfactant is preferably uniformly dispersed over the entire surface of the magnetic carrier. Here, in order to prevent charge-up, a method of dispersing conductive particles is also conceivable. However, when the conductive particles are used, the resistance value of the carrier particles rapidly decreases in proportion to the content of the particles, so that the induction charging phenomenon is promoted. That is, there is a trade-off relationship between suppression of charge-up and prevention of induction charging. On the other hand, when a surfactant having an antistatic effect is used, the decrease in the resistance value with respect to the same introduction amount is suppressed as compared with the conductive particles, and the generated charge is leaked while maintaining a relatively high resistance value. It has the feature of letting Therefore, both suppression of charge-up and prevention of induction charging can be achieved. Therefore, by using a surfactant having an antistatic effect, by using a surfactant having an antistatic effect, it is possible to suppress carrier charge-up without significantly reducing the resistance value. Deterioration can be prevented.

  In the image forming apparatus according to the present invention, in addition to the above-described configuration, the resistance layer may be subjected to antistatic processing.

  According to the above configuration, since the antistatic process is performed on the resistance layer, the magnetic carrier can be prevented from being charged up, and the magnetic carrier can be prevented from adhering to the image carrier. Further, since the charge-up of the resistance layer can be suppressed, it is possible to prevent the development electric field from being lowered and to ensure the electric field uniformity.

  As an antistatic process in the resistance layer, a surfactant having an antistatic effect may be dispersed in the resistance layer. In this case, the surfactant is preferably dispersed uniformly over the entire surface of the resistance layer. Here, the reason why the surfactant having an antistatic effect is used as the dispersed particles instead of the conductive particles is that the charge-up of the magnetic carrier can be suppressed without significantly reducing the resistance value.

  In the image forming apparatus according to the present invention, in addition to the above configuration, the resistive layer is made of a material having a high volume resistivity so that the volume resistance value is larger than the volume resistance value of the magnetic carrier in the developing nip portion. It may be.

  Here, the volume resistance value R is expressed by R = ρ × l / S from the volume resistivity ρ, the contact area S, and the thickness (resistance layer thickness) 1 of the resistance layer. Therefore, in order to increase the volume resistance value R, (1) increase the volume resistivity ρ, (2) decrease the contact area, or (3) increase the thickness of the resistance layer. Can do. Here, since the contact area is determined to some extent by the specifications of the image forming apparatus, it is difficult to control. Therefore, it is preferable to control by the volume resistivity or the thickness of the resistance layer. Here, in the image forming apparatus configured as described above, the resistance layer is made of a material having a high volume resistivity such that the volume resistance value is larger than the volume resistance value of the magnetic carrier in the developing nip portion. Therefore, according to the above configuration, it is not necessary to increase the thickness of the resistance layer when the volume resistance value is larger than the volume resistance value of the magnetic carrier in the development nip portion. The manufacturing cost of the developer carrier can be reduced.

  In the image forming apparatus according to the present invention, in addition to the above configuration, the thickness of the resistance layer is such that the volume resistance value of the resistance layer is larger than the volume resistance value of the magnetic carrier at the development nip portion. It may be a layer thickness.

  In the above configuration, the resistance layer has a layer thickness such that the volume resistance value of the resistance layer is larger than the volume resistance value of the magnetic carrier in the development nip portion. Therefore, according to the above configuration, when the volume resistance value is larger than the volume resistance value of the magnetic carrier in the development nip portion, the selectivity of the material constituting the resistance layer can be expanded. If a material close to the base material of the magnetic carrier surface layer in the charging sequence is selected as the material of the resistance layer, it is difficult to be affected by charge-up and a stable development electric field can be obtained.

  In the image forming apparatus according to the present invention, in addition to the above configuration, the resistance layer may contain the same material as the base material on the surface of the magnetic carrier.

  Here, it is assumed that the base material on the surface of the magnetic carrier is a material having the largest content among the materials included on the surface of the magnetic carrier. According to the above configuration, since the resistance layer on the surface of the developer carrier includes the same material as the base material of the magnetic carrier surface, frictional charging between the developer carrier and the magnetic carrier surface is suppressed. be able to. Accordingly, since the charge-up on the developer carrier surface and the magnetic carrier surface can be reduced, fluctuations in the developing electric field can be suppressed.

  In the image forming apparatus according to the present invention, as described above, the developer held on the developer carrier is in contact with the image carrier that faces the developer carrier on the sleeve surface. A resistance layer having a volume resistance value larger than the volume resistance value of the magnetic carrier at the developing nip portion, which is a region, is provided.

  According to the above configuration, by providing the resistance layer having a volume resistance value larger than the volume resistance value of the magnetic carrier at the development nip portion on the surface of the sleeve of the developer carrier, the image carrier and the developer carrier Can prevent inductive charging from occurring in the opposite development areas. Therefore, it is possible to suppress inductive charge injection from the developer carrier to the carrier due to the developing electric field acting on the development area where the image carrier and the developer carrier face each other. Since inductive charge injection into the magnetic carrier can be suppressed, adhesion of the magnetic carrier to the image carrier can be reduced. Since adhesion of the magnetic carrier can be reduced, it is possible to form an extremely high quality image free from image omission and image fogging. Also, since the magnetic restraint force is not increased as in the prior art, high-quality images can be formed without inducing streaking of developed images and shortening the life of magnetic carriers and image carriers. Can do.

  The embodiment of the present invention will be described below with reference to FIGS. Note that the present invention is not limited to this.

  FIG. 2 is a schematic diagram showing an outline of the main configuration of the image forming apparatus 1 of the present embodiment. As shown in FIG. 2, in the image forming apparatus 1, a two-component developer (developer) 12 composed of a magnetic carrier and a non-magnetic toner previously put in the developing tank 30 is stirred and charged by a stirring screw 31. The The two-component developer 12 is transported to the developer carrier 13 in which a magnet roller serving as a magnetic field generating means is disposed, and is held on the surface of the developer carrier 13 by a magnetic restraining force. Next, the two-component developer 12 held on the surface of the developer carrier 13 is regulated to a constant layer thickness by the layer regulating blade 32, and a magnetic brush is applied to the opposite portion between the developer carrier 13 and the image carrier 14. A visible image is formed by adhering only toner to the electrostatic latent image formed on the surface of the image carrier 14 by exposure means (not shown). Further, as shown in FIG. 1, since the magnet roller 100 provided in the developer carrying member 13 is a fixed member and the metal sleeve 102 is a rotating member, the developer carrying member 13 is provided with a gap 101 to avoid rubbing. It has been.

  In the image forming apparatus 1, the magnet roller disposed inside the developer carrier 13 is composed of a total of five poles, of which the developer carrier 13 and the image carrier 14 are located in the development region where they face each other. The magnetic flux density in the normal direction of the magnetic pole is assumed to be 110 [mT]. These numerical values are merely examples, and are not limited to these. Further, the gap between the developer carrier 13 and the image carrier 14 in the development region is set to 0.45 [mm] in this experimental example. Of course, this is also merely an example and is not limited to this value.

  Here, as shown in FIG. 1, a resistance layer 103 is formed on the surface layer of a metal sleeve (nonmagnetic sleeve) 102 of the developer carrier 13. The volume resistance value of the resistance layer 103 is determined at the development nip (region where the two-component developer 12 held on the developer carrier 13 is in contact with the image carrier 14 facing the developer carrier 13). The volume resistance value is larger than the volume resistance value of the magnetic carrier 10.

  As described above, in the image forming apparatus 1, a resistance layer having a volume resistance value larger than the volume resistance value of the magnetic carrier 10 in the development nip portion is provided on the surface of the metal sleeve 102 in the developer carrier 13. Further, induction charging can be prevented from occurring in the development area where the image carrier 14 and the developer carrier 13 face each other. Therefore, it is possible to suppress inductive charge injection from the developer carrier 13 to the magnetic carrier 10 due to the development electric field acting on the development region where the image carrier 14 and the developer carrier 13 face each other. Since inductive charge injection into the magnetic carrier can be suppressed, the image forming apparatus 1 can reduce carrier adhesion to the image carrier 14. Therefore, in the image forming apparatus 1, carrier adhesion can be reduced, so that it is possible to form an extremely high quality image free from image omission and image fogging. Further, since the image forming apparatus 1 does not increase the magnetic restraint force as in the conventional image forming apparatus, it does not induce a sweeping streak on the developed image and shortens the life of the carrier or the image carrier. A high quality image can be formed.

  Further, the resistance layer 103 may be subjected to antistatic processing. As this antistatic processing, as shown in FIG. 1, a surface active agent 104 having an antistatic effect is uniformly dispersed in the resistance layer 103 formed on the surface of the metal sleeve 102 on the developer carrier 13. May be. Alternatively, as the antistatic processing, it is desirable to apply an antistatic coating using a surfactant. Here, the surfactant having an antistatic effect instead of the conductive particles is used as the dispersed particles because the charge-up of the magnetic carrier 10 can be suppressed without significantly reducing the resistance value.

  As described above, since the antistatic process is performed on the resistance layer 103, the charge-up of the magnetic carrier 10 can be suppressed, and the magnetic carrier can be prevented from adhering to the image carrier. Furthermore, since the charge-up of the resistance layer 103 can be suppressed, it is possible to prevent the development electric field from being lowered and to ensure the electric field uniformity.

Next, a means for making the volume resistance value of the resistance layer 103 larger than the volume resistance value in the developing nip portion of the magnetic carrier will be considered. The volume resistance value R [Ω] is obtained by R = ρ · l / S from the volume resistivity ρ [Ω · cm], the contact area S [cm ² ], and the layer thickness l [cm] of the resistance layer. Here, since the contact area is determined to some extent by the specifications of the image forming apparatus, it is difficult to control. Therefore, the volume resistance value can be controlled by the volume resistivity ρ and the layer thickness l of the resistance layer, excluding the contact area S.

  First, in the case where the volume resistivity R is controlled by the volume resistivity ρ, a material having a high volume resistivity such that the volume resistivity is larger than the volume resistivity of the magnetic carrier 10 at the development nip portion as the resistance layer 103. May be used. By using such a material having a high volume resistance value, it is not necessary to increase the thickness of the resistance layer 103 more than necessary. Therefore, the material cost for forming the resistance layer 103 and the manufacturing cost of the developer carrier 13 can be suppressed.

  Next, when the volume resistance value R is controlled by the layer thickness l of the resistance layer, the selectivity of the material constituting the resistance layer 103 is widened, and a material close to the base material of the magnetic carrier 10 surface layer can be selected in the charging sequence. Therefore, it is difficult to be affected by the charge-up and a stable development electric field can be obtained.

  Further, it is desirable that the resistance layer 103 formed on the surface layer of the metal sleeve 102 contains the same material as the base material having the highest content among the materials contained in the coating layer of the magnetic carrier. This is because, when considering the contact triboelectric charge between the carrier coating layer and the resistance layer, it is more difficult for the charged charges to be generated if they contain the same material, and even if they occur, different materials were used. Since it is a small amount compared to the case, it is less susceptible to charge-up. That is, it is difficult for the charged charges to be deposited on the carrier or the resistance layer, and it is possible to suppress density fluctuation or density unevenness due to fluctuation of the developing electric field due to charge-up, and carrier adhesion to the image carrier due to carrier charging. Therefore, a good quality image can be formed.

  As for the magnetic carrier 10 used in the image forming apparatus 1 of the present embodiment, as shown in FIG. 3, a coating layer in which a surfactant 91 having an antistatic effect is dispersed on the surface of the core 90 of the magnetic carrier 10. 92 may be provided. Alternatively, an antistatic coating using a surfactant may be applied. As the surfactant used here, a cationic surfactant having an excellent antistatic effect is preferable. Specific examples include alkyl trimethyl ammonium salts, monoalkyl ammonium chlorides, dialkyl ammonium chlorides and the like. However, it is not limited to these.

  Here, in order to prevent charge-up, a method of dispersing conductive particles is also conceivable. However, when the conductive particles are used, the resistance value of the carrier particles rapidly decreases in proportion to the content of the particles, so that the induction charging phenomenon is promoted. That is, there is a trade-off relationship between suppression of charge-up and prevention of induction charging. On the other hand, the surfactant having the antistatic effect is that the decrease in the resistance value with respect to the same introduction amount is suppressed as compared with the conductive particles, and leaks the generated charges while maintaining a relatively high resistance value. Has characteristics. Therefore, it is possible to achieve both suppression of charge-up and prevention of induction charging by using a surfactant having an antistatic effect. Therefore, by using a surfactant having an antistatic effect, it is possible to suppress the charge-up of the magnetic carrier 10 without significantly reducing the resistance value of the magnetic carrier 10, and to prevent image quality deterioration.

(Experimental example 1)
In this experimental example, first, the configuration of the image forming apparatus 1 described above with reference to FIG. 2 is used as an image forming apparatus in order to verify the influence of the coating applied to the magnetic carrier on the induction charging of the magnetic carrier. In the same manner as that described above, but the resistance layer 103 is not provided on the surface of the developer carrier 13.

  Here, in the image forming apparatus of this experimental example, the magnet roller disposed inside the developer carrying member 13 is composed of a total of five poles, of which the developer carrying member 13 and the image carrier 14 are opposed to each other. The magnetic flux density in the normal direction of the magnetic pole located in the region is assumed to be 110 [mT]. These numerical values are merely examples, and are not limited to these. Further, the gap between the developer carrier 13 and the image carrier 14 in the development region is set to 0.45 [mm] in this experimental example. Of course, this is also merely an example and is not limited to this value.

  In this experimental example, when an image forming apparatus is used and only a carrier is put into the developing tank 30 and a potential difference is provided between the developer carrier 13 and the image carrier 14 to rotate them, the image carrier is used. FIG. 4 shows the result of measuring the number of carriers per sheet of A4 paper attached to 14. In this experimental example, a ferrite carrier containing Mg having a volume average particle size of 55 [μm] and a saturation magnetization of 65 [emu / g] is used as the magnetic carrier 10, and coating 1, coating 2, and coating 3 are different on the carrier surface. A coated one was used. In this experimental example, the materials of the coatings 1 to 3 are all silicone-based resins and have a thickness of 1 μm. And the coating uses the immersion method. Of course, it may be coated by other methods.

Here, as described above, the developing bias is V _OPC −V when the surface potential of the image carrier 14 is V _OPC and the voltage applied to the metal sleeve 102 of the developer carrier 13 is V _dev. It is a value represented by _dev . That is, the positive bias area indicates an image area (black solid image area), and the negative bias area indicates a non-image area (background area).

  As can be seen from FIG. 4, first, when the magnetic carrier of the coating 1 is used, the number of adhered carriers increases rapidly as the bias absolute value increases in both the image area and the non-image area. This means that carrier adhesion due to induction charging phenomenon is induced. Next, it can be seen that when the magnetic carrier of coating 2 is used, the number of carrier adhesions in both the image area and the non-image area is greatly reduced as compared with the magnetic carrier of coating 1. In particular, it can be seen that the bias dependence is extremely small in the non-image region. In addition, when the magnetic carrier of the coating 3 is used, it can be seen that the number of adhered carriers is further reduced as compared with the magnetic carrier of the coating 2, and in particular, the number of adhered carriers in the image region is rapidly decreased.

  Here, the volume resistivity was measured for each of the magnetic carriers of coating 1, coating 2, and coating 3, and the correlation with the number of adhered carriers was examined. A method for measuring the volume resistivity will be described with reference to FIG. Using the image forming apparatus 5 shown in FIG. 5, only the magnetic carriers 10 with coatings 1 to 3 are put into the developing tank 30. Then, the developer carrier 13 holding the magnetic carrier 10 on the surface is opposed to the aluminum element tube 50 on which the photosensitive layer is not formed. Next, a potential difference V is provided by a DC power source between the developer carrier 13 and the aluminum base tube 50, and when the developer carrier 13 is rotated while the aluminum base tube 50 is stationary, the magnetic brush 51 is moved. The current I flowing through the formed magnetic carrier is read from the ammeter 52. Then, the volume resistance value R of the carrier is obtained from Ohm's law. Here, as shown in FIG. 6, when the nip width at the development nip is a [cm], the depth is b [cm], and the development gap is 1 [cm], the volume resistivity ρ of the magnetic carrier 10 at the development nip is ρ. [Ω · cm] is obtained by ρ = R × a × b / l.

  FIG. 7 shows the results of measuring the volume resistivity of the magnetic carrier coated with each of coating 1, coating 2, and coating 3 by the above method. Here, the applied voltage refers to a potential difference V provided between the developer carrier 13 and the aluminum base tube 50. As can be seen from FIG. 7, the magnitude relationship of the volume resistance values is coating 1 <coating 2 <coating 3. Referring to FIG. 4, it can be seen that the magnetic carrier of coating 1 having the largest number of carriers attached has the lowest volume resistivity, and the magnetic carrier of coating 3 having the smallest number of carriers attached has the highest volume resistivity. Therefore, it can be seen that the use of a magnetic carrier having a higher volume resistivity can suppress charge injection due to induction charging and can reduce carrier adhesion to the image carrier.

Here, from the relationship between the number of adhered carriers and the volume resistivity, having a volume resistivity equal to or higher than the magnetic carrier of the coating 2 is effective for reducing carrier adhesion. That is, it is desirable that the coating 2 carrier has a volume resistivity of 2.2 × 10 ¹⁰ [Ω · cm] or more, which is a volume resistivity when a DC voltage of 100 V is applied. Furthermore, it is more preferable that the volume resistivity of the magnetic carrier of the coating 3 exceeds 1.2 × 10 ¹² [Ω · cm].

  Here, although the resin material and the thickness are the same, the difference in resistance value between the magnetic carriers of coatings 1 to 3 is considered to be due to the difference in the uniformity of the coating layer. Specifically, the resistance value is higher in the case of uniform coating, and therefore, the uniformity seems to be higher in the order of coating 1 <coating 2 <coating 3. In addition, it is thought that the cause of the difference in the uniformity of the coating is caused by a difference in molecular weight or a difference in curing method.

(Experimental example 2)
Next, in this experimental example, as a means for suppressing induction charging to the magnetic carrier, the effect of providing the resistance layer 103 on the surface of the developer carrier 13 in order to suppress the flow of electric charge from the developer carrier 13. Verified. The magnetic carrier 10 used in this experimental example has a volume resistance value lower than that of the magnetic carrier coated with the three types of coatings in experimental example 1, the saturation magnetization is 65 [emu / g], and the volume average particle diameter is 55. The thing of [micrometer] was used. The coating material is a silicone resin, the coating thickness is 0.5 μm, and the coating uses an immersion method. The reason why the volume resistance value is lower than that of the magnetic carrier obtained by coating each of the three coatings in Experimental Example 1 is considered to be because the coating layer is thin.

Further, the examination machine used for the examination in this experimental example is not the image forming apparatus 5 shown in FIG. 5, but an aluminum flat plate having a magnetic field generating means arranged at the bottom as a developer carrier, and a resistance layer on the flat plate surface. A film tape made of stretched polypropylene (OPP) having a volume resistivity of 1.0 × 10 ¹⁶ [Ω · cm] and a thickness of 40 μm is pasted. A carrier brush was formed on such a developer carrying member to form a magnetic brush and contacted with a cylindrical photosensitive drum to measure the amount of carrier adhesion when a potential difference was applied. Note that the magnetic flux density in the normal direction of the magnetic field generating means in this examination machine was 76 [mT], and the gap between the aluminum flat plate and the photosensitive drum was 0.45 [mm].

  FIG. 8 shows the result of measurement of the carrier adhesion amount. It can be seen that the number of carriers adhering per unit area can be reduced in both the image area and the non-image area when the resistance layer is provided compared to the case where the resistance layer is not provided on the aluminum flat plate.

  Therefore, it can be seen that by providing a resistance layer on the surface of the developer carrier, the induction charging phenomenon can be suppressed, carrier adhesion to the image carrier is reduced, and image quality can be improved.

  The film tape used in the examination machine described above has a volume resistance value R [Ω] obtained from the volume resistivity ρ [Ω · cm] larger than the volume resistance value of the magnetic carrier. The same examination was performed using a film tape having a small volume resistance value. As a result, there was no significant difference in the number of carrier deposits compared to the case where no resistance layer was provided, and the carrier deposition reduction effect could not be confirmed. Therefore, it can be seen that the resistance layer provided on the surface of the developer carrier preferably has a larger volume resistance value than the magnetic carrier.

  As can be seen from Experiment 1 and Experiment 2, in the image forming apparatus 1, the magnetic carrier 10 has a high resistance, and the resistance layer 103 having a volume resistance higher than that of the magnetic carrier 10 in the development nip portion is provided on the surface of the metal sleeve 102. Thus, it was found that the adhesion of the carrier to the image carrier 14 is reduced. However, by making these high resistances, there is a possibility that a negative effect due to improvement of charge retention may occur. That is, charge-up due to contact friction between the magnetic carrier 10 and the developer carrier 13, the image carrier 14, and the toner 11 and charge-up due to contact friction between the resistance layer 103 and the magnetic carrier 10 are likely to occur. There is a concern that electric field fluctuations occur in the development region. As a result, there is a possibility that density fluctuation, density unevenness, carrier adhesion to the image carrier, etc. may occur, making it difficult to obtain good image quality. Therefore, it is preferable to take measures against charge-up on both the magnetic carrier 10 and the resistance layer 103.

  With respect to the magnetic carrier 10, as shown in the embodiment, as shown in FIG. 3, a coating layer 92 in which a surfactant 91 having an antistatic effect is dispersed is provided on the surface of the core 90 of the magnetic carrier 10. Alternatively, it is preferable to apply an antistatic coating using a surfactant. The surfactant used here is preferably a cationic surfactant having an excellent antistatic effect, and specific examples thereof include alkyltrimethylammonium salts, monoalkylammonium chlorides, dialkylammonium chlorides and the like. A surfactant having an antistatic effect is characterized in that a decrease in resistance value with respect to the same introduction amount is suppressed as compared with conductive particles, and a generated charge is leaked while maintaining a relatively high resistance value. Therefore, both suppression of charge-up and prevention of induction charging can be achieved. Therefore, by using a surfactant having an antistatic effect, carrier charge-up can be suppressed and image quality deterioration can be prevented without significantly reducing the resistance value.

  As for the resistance layer, as shown in the embodiment, as shown in FIG. 1, the resistance layer 103 is uniformly dispersed with a surfactant 104 having an antistatic effect, or a surfactant is used. It is desirable to apply an antistatic coating.

  Next, in order to make the volume resistance value of the resistance layer 103 larger than the volume resistance value in the developing nip portion of the magnetic carrier 10, as shown in the embodiment, as one method, A material having a high volume resistivity, such that the volume resistance value is larger than the volume resistance value of the magnetic carrier 10 at the development nip portion, may be used. By using a material having a high volume resistance value, it is not necessary to increase the thickness of the resistance layer 103 more than necessary. Therefore, it is possible to reduce the material cost of the resistance layer 103 and the manufacturing cost of the developer carrier 13. . As another method, the volume resistance value R can be controlled by the layer thickness l of the resistance layer. In this case, the selectivity of the material constituting the resistance layer 103 is widened, and a material close to the base material of the surface of the magnetic carrier 10 can be selected in the charging order. Obtainable.

  Further, it is desirable that the resistance layer 103 formed on the surface layer of the metal sleeve 102 can include the same material as the base material having the highest content among the materials included in the coating layer of the magnetic carrier 10. This is because, when considering the contact triboelectric charge between the coating layer of the magnetic carrier 10 and the resistance layer 103, it is more difficult for the charged charges to be generated if they contain the same material, and even if they occur, the generated amounts are different from each other. This is because the amount is small compared to the case of using, so that it is not easily affected by charge-up. That is, it is difficult for charged charges to be deposited on the magnetic carrier 10 or the resistance layer 103, density fluctuation or density unevenness due to fluctuations in the developing electric field due to charge-up, and carrier adhesion to the image carrier 14 due to charging of the magnetic carrier 10. Since it can suppress, a quality image can be obtained.

  The present invention is not limited to the above-described embodiments and experimental examples, and various modifications can be made within the scope indicated in the claims. That is, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

The image forming apparatus of the present invention may be expressed as an image forming apparatus having the following configuration. That is, a permanent magnet as a magnetic field generating means is disposed inside, and a magnetic carrier and a nonmagnetic toner are provided on the surface of a developer carrier having a nonmagnetic metal sleeve that can rotate independently of the permanent magnet. In the image forming apparatus that holds the constituted two-component developer and visualizes the electrostatic latent image formed on the surface of the image carrier by the two-component developer, the magnetic carrier includes the image carrier and the image carrier. A volume resistivity determined from a dynamic resistance value measured under application of a DC voltage of 100 V in a region facing the developer carrier is 2.2 × 10 ¹⁰ Ω · cm or more, and the developer carrier In the image forming apparatus, a resistance layer having a larger volume resistance value than the magnetic carrier is provided on the surface of the metal sleeve.

  Further, in the image forming apparatus, in addition to the above configuration, a coating layer in which a surfactant having an antistatic effect is uniformly dispersed over the entire surface of the magnetic carrier is formed on the surface, or The antistatic coating may be applied uniformly over the entire surface.

  In the image forming apparatus, in addition to the above configuration, a surfactant having an antistatic effect is uniformly dispersed over the entire surface of the resistive layer, or an antistatic coating is uniformly applied over the entire surface. You may give it.

  In addition to the above configuration, the image forming apparatus uses a material having a high volume resistivity as a base material of the resistance layer as means for increasing the volume resistance value of the resistance layer larger than the volume resistance value of the magnetic carrier. May be.

  In addition to the above configuration, the image forming apparatus may increase the thickness of the resistance layer as a means for increasing the volume resistance value of the resistance layer larger than the volume resistance value of the magnetic carrier.

  In the image forming apparatus, in addition to the above configuration, the resistance layer may contain the same material as the base material of the outermost layer of the magnetic carrier.

  The image forming apparatus of the present invention can be widely applied to, for example, a laser printer, a copying machine, a multifunction machine, etc. to which an electrophotographic image forming system using a two-component developer containing a magnetic carrier is applied.

FIG. 3 is a schematic configuration diagram illustrating an example of a configuration of a developer carrier provided with a resistance layer and a magnetic carrier in the image forming apparatus according to the present invention. 1 is a schematic diagram illustrating an outline of a main configuration of an image forming apparatus according to the present invention. It is a schematic block diagram which shows an example of the internal structure of the magnetic carrier used for the image forming apparatus which concerns on this invention. It is a figure which shows the result of having measured the developing bias dependence of the carrier adhesion number per A4 paper in the image carrier surface about the magnetic carrier which gave different coating with respect to the same core. It is a schematic diagram which shows the outline | summary of the main structures of the measurement system used for volume resistivity derivation | leading-out of a magnetic carrier. It is a supplementary figure at the time of explaining the process of deriving the volume resistivity of a magnetic carrier. It is a figure which shows the applied voltage dependence of volume resistivity about the magnetic carrier which gave different coating with respect to the same core. FIG. 6 is a diagram showing the results of measuring the development bias dependence of the number of carriers deposited per unit area on the surface of the image carrier when the resistance layer is formed on the surface of the developer carrier and when the resistance layer is not formed. FIG. 6 is a diagram for explaining an induction charging phenomenon caused by an electric field acting between a developer carrier and an image carrier in an image forming apparatus using a conventional two-component developer. FIG. 6 is a diagram showing the development bias dependence of the number of carriers attached per A4 sheet on the surface of an image carrier when an image forming apparatus using a conventional two-component developer is used.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Magnetic carrier 11 Toner 12 Two-component developer (developer)
DESCRIPTION OF SYMBOLS 13 Developer carrier 14 Image carrier 50 Aluminum elementary tube 52 Ammeter 90 Core 91 Surfactant with antistatic effect 92 Coating layer 100 Magnet roller 101 Gap 102 Metal sleeve 103 Resistance layer 104 Interfacial activity with antistatic effect Agent

Claims (9)

A developer containing a magnetic carrier and a non-magnetic toner is held on the surface of a developer carrying member provided with a magnetic non-magnetic sleeve and having a rotatable non-magnetic sleeve. In the image forming apparatus that visualizes the electrostatic latent image formed in
On the sleeve surface, the volume resistance of the magnetic carrier at the developing nip portion, which is a region where the developer held on the developer carrier is in contact with the image carrier facing the developer carrier. An image forming apparatus, wherein a resistance layer having a volume resistance value larger than the value is provided. The magnetic carrier has a volume resistivity of 2.2 × 10 ¹⁰ Ω · cm or more obtained from a dynamic resistance value measured under application of a DC voltage of 100 V at the development nip portion. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the magnetic carrier is subjected to antistatic processing.   The image forming apparatus according to claim 3, wherein a coating layer in which a surfactant having an antistatic effect is dispersed is formed on the surface of the magnetic carrier.   The image forming apparatus according to claim 1, wherein the resistance layer is subjected to antistatic processing.   The image forming apparatus according to claim 5, wherein a surfactant having an antistatic effect is dispersed in the resistance layer.   The said resistance layer consists of a material with a high volume resistivity so that a volume resistance value may become larger than the volume resistance value of the magnetic carrier in the said development nip part. The image forming apparatus described in 1.   The layer thickness of the resistance layer is a layer thickness such that a volume resistance value of the resistance layer is larger than a volume resistance value of a magnetic carrier in the development nip portion. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the resistance layer contains the same material as the base material on the surface of the magnetic carrier.

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