JP2005275127A - Developing device and image forming device having same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve both of prevention of edge thinning and suppression of fogging and to enhance feeding capabilities of developer in performing non-contact development by feeding of the developer using progressive electric fields. <P>SOLUTION: In a system for performing the non-contact development by using a developer feeding member 41 having a plurality of progressive wave generation electrodes 41b and feeding the developer toward a photoreceptor drum 1 by the progressive electric fields formed by the developer feeding member, both of the prevention of edge thinning and the suppression of fogging are achieved by setting a development gap G(mm) at a position where the developer feeding member 41 and the photoreceptor drum 1 approach most, arrangement pitch λ(mm) of the progressive wave generation electrode and dielectric thickness A(mm) on the progressive wave generation electrode so as to satisfy relation of [0.5<λ/G<2] and [5×A<λ] and optimizing development conditions. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device and an image forming apparatus that develop an electrostatic latent image formed on an image carrier with a developer, and in particular, the developer is transported using a traveling wave electric field to be formed on the image carrier. The present invention relates to a developing device that visualizes a developed electrostatic latent image, and an image forming apparatus including the developing device.

  Further, according to the present invention, the electrostatic latent image is not limited to the one in which optical information is written on the image carrier charged with a predetermined charge, but the electrostatic charge is directly applied on the dielectric as in the ion flow method. The present invention can also be applied to an apparatus that forms a latent image.

  As a developing device applied to an image forming apparatus using an electrophotographic process such as a copying machine or a printer, a non-contact developing device that performs development without bringing a developer carrier into contact with an image carrier is currently attracting attention. A method using a powder cloud method, a jumping method, or an electric field curtain (traveling wave electric field) has been proposed.

  As an apparatus using an electric field curtain, for example, a power source that generates a plurality of types of alternating voltages having different phases from each other, and an alternating voltage from the power source are applied to a plurality of electrodes arranged at predetermined intervals on a substrate. There has been proposed a developing device including a developer transport member that transports a developer toward an image carrier by forming a traveling-wave electric field by applying (see, for example, Patent Document 1 and Patent Document 2). ).

  Further, regarding a technique using a traveling wave electric field, the applicant of the present invention sets the relationship between the developing gap d between the developer carrying member and the image carrier and the inter-electrode pitch λ on the developer carrying member as d> λ. A developing device for improving image uniformity (see, for example, Patent Document 3), and setting of a developing gap, a photosensitive member film thickness, a developing potential condition, and the like for the purpose of reducing the edge effect and improving the image quality. It is proposed to do this (see, for example, Patent Document 4).

Further, the applicant of the present invention supplies a developer directly on a developer conveying member made of an FPC (flexible circuit board) or the like, and a problem in the developer conveying method using a traveling wave electric field generated from the developer conveying member. As a method for solving this problem, the developer is supplied by a belt member that moves in the developer conveying direction while covering the developer conveying member, and the surface of the belt member is always refreshed by the cleaning member. Has proposed a developing device that can stabilize the developer conveying function (see, for example, Patent Document 5).
Japanese Examined Patent Publication No. 5-31146 (Specification, page 2, right column, line 20 to page 3, right column, line 5, FIGS. 1 and 2) Japanese Examined Patent Publication No. 5-31147 (page 2 left column, line 29 to page 4, right column 21 line, FIGS. 1 and 2) JP 2003-5524 A JP 2003-228236 A JP 2002-91160 A (paragraphs [0032] to [0034], FIG. 2)

  By the way, when the toner is transported in a cloud state by a traveling wave electric field and development is performed in a non-contact state with the image carrier, the following problems occur depending on the toner transport conditions and the development gap setting.

  In recent years, high-quality image forming apparatuses comparable to photographs typified by inkjet printers have been developed, and higher image quality is also required in image formation using toner. In addition, in order to save energy in the fixing process, reduce running cost, and further reduce the size of the apparatus by reducing the volume of the toner container, attempts have been made to reduce toner consumption while maintaining a necessary concentration. . One technical approach to achieve this is to reduce the toner particle size and increase the content of colorant (for example, carbon black, organic pigment, etc.) in the toner. Therefore, there is a trend to form a higher quality image by reducing the thickness of the image. In performing such image formation, it is necessary to uniformly develop a thin layer of a smaller amount of toner than in the past in the stage of forming a toner image on the photoreceptor.

As a result of research conducted by the present inventors, a new problem has been found that arises by developing a thin layer in an amount approximately corresponding to one or two toner layers. The amount of toner developed on the photoconductor during thin layer development here is about R × 0.1 (mg / cm ² ) or less, where R (μm) is the volume average particle diameter of the toner. Japanese Patent Application Laid-Open No. H10-228561 describes an idea that mainly suppresses a phenomenon in which toner gathers at a latent image edge portion and the outline of an image becomes thick when the development gap is too wide. In the case where the amount of toner to be developed is relatively large, basically a good result is obtained by setting conditions in the direction of narrowing the development gap.

  However, as described above, in the development of a thin layer, even in a proper range, under a relatively wide development gap condition, the vicinity of the edge of the image is not developed, and the contour portion of the image can be lost. 4 may exhibit the opposite behavior to the technique described in 4. In addition, as a measure for reducing the thinning phenomenon at the edge when such thin layer development is performed, it is effective to set conditions for further narrowing the development gap.

  On the other hand, in Patent Document 3 described above, the development gap is made larger than the electrode pitch of the developer conveying member, thereby suppressing density unevenness caused by the change in voltage applied to each electrode and suppressing background fogging. The idea to do is disclosed. Therefore, in order to narrow the development gap in order to reduce edge thinning, it is necessary to set the pitch between the electrodes of the developer conveying member to be narrow, which causes a problem that the toner conveying ability is lowered.

  The present invention has been made in view of such circumstances, and at the time of developing by non-contact development by toner conveyance using a traveling wave electric field, while achieving both prevention of edge thinning and suppression of fogging, It is an object to provide a developing device capable of enhancing the conveyance capability and an image forming apparatus that includes the developing device having such characteristics and can obtain a high-quality image while suppressing consumption of the developer. To do.

  The developing device of the present invention is a developing device for developing an electrostatic latent image formed on the surface of an image carrier with a developer, and a plurality of traveling waves arranged at predetermined intervals on a substrate. A developer conveying member that has a generation electrode and conveys the developer toward the image carrier by a traveling wave electric field formed by applying a plurality of types of alternating voltages having different phases to the traveling wave generation electrode. The developing gap at the position where the developer conveying member and the image carrier are closest to each other is G (mm), and the arrangement pitch of the traveling wave generating electrodes of the developer conveying member is λ (mm). ), Where the dielectric thickness on the traveling wave generating electrode of the developer conveying member is A (mm), the relationship of [0.5 <λ / G <2] and [5 × A <λ] is satisfied. It is a feature.

  The developing device of the present invention is a developing device for developing an electrostatic latent image formed on the surface of an image carrier with a developer, and a plurality of traveling waves arranged at predetermined intervals on a substrate. A developer conveying member that has a generation electrode and conveys the developer toward the image carrier by a traveling wave electric field formed by applying a plurality of types of alternating voltages having different phases to the traveling wave generation electrode. And a belt member that covers the surface of the developer conveying member and moves on the surface in the developer conveying direction. A developer layer is formed on the belt member, and the developer is transferred to the developer conveying member. In the developing device configured to transfer to a region where a traveling wave electric field is formed, a developing gap at a position where the belt member and the image carrier are closest to each other is G (mm), and the developer is conveyed. Traveling wave generator for members Is 0.5 (λ), the dielectric thickness on the traveling wave generating electrode of the developer conveying member is A (mm), and the thickness of the belt member is B (mm) [0.5 <λ / It is characterized by satisfying the relationship of G <2] and [5 × (A + B) <λ].

  In the developing device of the present invention, the contact angle with respect to water of the surface of the developer conveying member on which the developer is conveyed, or the contact angle with respect to water of the surface on which the developer layer of the belt member is formed is 85 ° or more. Preferably there is.

  In the developing device of the present invention, it is preferable that a surface of the developer transport member on which the developer is transported or a surface on which the developer layer of the belt member is formed contains a fluorine-based substance.

  In the developing device of the present invention, fine particles are dispersed in the dielectric layer on the traveling wave generating electrode of the developer conveying member or the belt member, and some of the fine particles are exposed on the surface. Preferably it is. When the fine particles are dispersed, it is preferable that the relationship [r1 <r2] is satisfied, where r1 is the volume average particle size of the fine particles and r2 is the volume average particle size of the developer. The fine particles are preferably a fluorine-based substance.

  In the developing device of the present invention, it is preferable that the dielectric layer on the traveling wave generating electrode of the developer conveying member or the belt member is composed of at least two layers of materials.

In the developing device of the present invention, the amount of developer developed on the image carrier (particularly, the amount of developer when forming a solid image) is mo (mg / cm ² ), and the volume average particle diameter of the developer is r2 ( μm), it is preferable to satisfy the relationship [mo ≦ 0.1 × r2].

  An image forming apparatus according to the present invention includes an image forming unit that forms an image based on image data, and a developing device having the above-described characteristic configuration.

  Hereinafter, the present invention will be described in detail.

  First, in the developing method applied to the present invention, that is, in the method of developing the electrostatic latent image on the photosensitive member by keeping the toner as a developer in a cloud state and keeping it in a non-contact state with respect to the photosensitive member (image carrier). Compared with the contact-type development method, the binding force on the toner itself is very small. Therefore, even when a minute electrostatic latent image is formed on the photoreceptor, it is easy to react to a weak electric field in the vicinity of the photoreceptor, and the development characteristics of minute dots and line patterns are excellent. Further, in such a minute pattern, the development performance of dots and lines can be enhanced by the action of the so-called edge effect around the lines of electric force around the latent image. However, while having such characteristics, the following problems may occur.

  That is, as shown in FIG. 7, when a pattern having a relatively low spatial frequency, such as a solid patch, is formed, if the development gap is too wide, a large wraparound of the lines of electric force occurs around the latent image edge, resulting in a strong edge effect. Appears. The toner is clouded by the traveling wave electric field, and the wraparound electric field acts on the latent image edge portion in the developing gap where the toner moves from the developer conveying member to the photosensitive member, and the flying trajectory of the toner is deflected. Accordingly, when moving in the development gap, the toner moves so that the toner can easily gather inside the latent image edge portion.

  Further, in the vicinity of the surface of the photosensitive member, a horizontal electric field acts strongly, and toner hardly enters the region where the electric lines of force around the latent image edge portion wrap around. However, under conditions where the amount of toner supply is relatively large, the toner enters the region where the lines of electric force are wrapping around with a certain probability. Once the toner enters this region, the intruding toner is strongly restrained by the wraparound electric field, and concentrates on the contour portion of the latent image to create a state where the image contour becomes dark (see FIG. 8A).

  In order to solve such a phenomenon, the present applicant has proposed to appropriately set the relationship between the photoreceptor film thickness and the development gap (Patent Document 4). This proposed technique basically sets the developing gap in a narrowing direction so that the thinner the photoreceptor film thickness is, the more the condition is narrowed.

  However, as a result of diligent research by the present inventors, it has been found that the following problems occur when forming a thinner image by reducing the amount of toner developed on the photoreceptor.

  That is, under the condition where the amount of supplied toner is relatively large, the toner slightly enters the latent image edge portion. However, under the condition where the amount of toner used for development on the photosensitive member is small, such an action is poor, and the latent image edge portion. It was found that the phenomenon of “edge thinning” in which toner does not adhere to the toner occurs (see FIG. 8B).

  Further research was conducted to eliminate this edge thinning, and it was found that it was effective to further narrow the development gap. This is considered to have the following effects.

  That is, by further narrowing the development gap, the time affected by the deflection electric field in the development gap is shortened, and the voltage applied to each electrode that generates the traveling wave electric field instantaneously moves to the photoreceptor side. It is presumed that the generation of a strong electric field that pushes the toner causes an action of pushing the toner into the edge portion of the latent image (see FIGS. 9A and 9B).

  Even in a general development method, the edge effect is reduced by narrowing the development gap, that is, by bringing the counter electrode facing the photoconductor closer, but in this case, a spatially uniform potential is applied to the counter electrode. As in the electric field curtain method, the above-mentioned action does not work by applying a temporally and spatially changing voltage, and the behavior differs from the action in the conventional developing method. .

  However, when the development gap is extremely narrowed, as described above, the influence of the voltage applied to each electrode also acts on a portion that is originally a non-image region, and the tendency to cause background fogging becomes remarkable. This is because the potential applied to each electrode of the developer conveying member is higher than the non-image portion potential of the photosensitive member, and if the photosensitive member is close to the developer conveying member, the non-image portion is also affected. This is a phenomenon in which a toner having a predetermined polarity is developed. Such a phenomenon is more likely to occur as the electrode pitch is wider.

  In addition, under conditions where the electrode pitch is wide, it is necessary to increase the amplitude of the applied voltage applied to the developer conveying member in order to obtain the electric field strength necessary for conveying the toner, and fog is more likely to occur. There is a tendency (see FIG. 10A).

  From the above, when narrowing the development gap, it is desirable to set the condition (see FIG. 10B) that the electrode pitch in the developer transport member is narrowed. However, in this case, the toner transport capability is reduced. A problem occurs.

  In addition, a dielectric layer is provided on the electrode in the developer conveying member on the surface of the developer conveying member in order to suppress leakage between adjacent electrodes and toner adhesion. When the relationship between the thickness and the size of the electrode pitch is not appropriate, the toner transport electric field strength on the surface of the developer transport member cannot be sufficiently expressed.

  Furthermore, when toner is transported by a traveling wave electric field, the toner may adhere to the developer transport member over time, or charging may occur due to contact between the toner and the above-described dielectric layer on the developer transport member. . These phenomena may impair the stability and uniformity of toner conveyance.

  In order to solve this problem, the present applicant arranges the endless belt member so as to cover the surface of the developer conveying member as described above, and rotates the belt member at a low speed, thereby changing the toner conveying surface. It has been proposed that the toner is always kept clean and the toner transportability is stabilized (Patent Document 5). However, in this proposed technique, it is necessary to select the electrode pitch in consideration of the thickness of the belt member in addition to the above-described dielectric layer thickness.

  In other words, in order to realize all of the above-mentioned problems such as prevention of edge thinning, suppression of fogging, and toner transportability, the relationship between the development gap, the electrode pitch, the dielectric layer thickness of the developer transport member, and the thickness of the belt member Must be selected appropriately. Therefore, when these appropriate relationships were investigated, results as shown in FIGS. 15 and 16 were obtained.

  FIG. 15 shows an evaluation of the image forming state when the developer transport member having three types of electrode pitch is used and the development gap is changed. Here, the degree of edge thinning and the state of fogging are evaluated with respect to the value [λ / G value] obtained by dividing the electrode pitch λ (μm) by the development gap G (μm).

  As is clear from the results of FIG. 15, the larger the λ / G, the smaller the development gap, but at this time, the edge thinning tends to decrease. Further, the smaller the λ / G value, the relatively larger the development gap. At this time, the fog tends to decrease. That is, it can be seen that the change in the λ / G value exhibits a behavior in which the degree of reduction of edge thinning and the degree of fog suppression are contradictory. It can also be seen that when the electrode pitch λ is changed, the development gap value giving an arbitrary λ / G value changes.

  Then, from the result of FIG. 15, when looking at the range of λ / G value indicating a good state with respect to the edge thinning and fogging, it is preferable that the range is larger than about 0.5 and smaller than 2. It can be seen that this is an image forming condition. That is, it is shown that the edge gap can be prevented and the fog can be suppressed by making the developing gap G half or twice of the electrode pitch λ.

  FIG. 16 shows the result of examining the toner transport performance with respect to the relationship between the dielectric layer thickness A (μm) on the developer transport member and the belt member thickness B (μm) with respect to the electrode pitch λ (μm). It is.

  Here, as a condition for changing the dielectric layer thickness, the dielectric layer is formed of a 12.5 μm polyimide film and a 15 μm adhesive layer to have a total thickness of 27.5 μm, and the polyimide film thickness is 25 μm. In the same manner, a layer having a thickness of 40 μm was formed. Further, a polyimide ink (dielectric ink) was printed on the electrode, and this was baked at about 400 ° C. and directly formed without an adhesive layer. Three types having a size of 12 μm were used. As for the belt member, a polyimide film tube having a thickness of 12.5 μm, 19 μm, 31 μm, 60 μm, and 150 μm was used (see FIGS. 11A to 11C).

  By combining these dielectric layers and belt members, the relationship between the electrode pitch λ and the A + B value (B = 0 when no belt member is used) was examined, and the toner conveyance efficiency was evaluated (FIG. 12A). (See (b)). However, with regard to toner conveyance efficiency, the phenomenon that the toner adheres to the developer conveyance member without being conveyed due to the traveling wave electric field, or in the system using the belt member, the supply formed on the belt member It was evaluated whether or not the toner can be conveyed by a traveling wave electric field with almost no excess.

  Further, as another evaluation of the conveyance performance, the uniformity of the toner conveyance state was evaluated. When the toner transport electric field works well, the toner behavior similarly occurs in the longitudinal direction with respect to the action of the traveling wave electric field, resulting in a uniform transport state.

  However, when the transport electric field is insufficient, there may be a phenomenon that even if the toner moves in an arbitrary place, the transport is not started in another place. That is, in such a case, the space density of the toner cloud when the toner is being conveyed is non-uniform, and if development is performed on the photoconductor in such a state, the development becomes a streak-like or spotted uneven state. This is an investigation of the occurrence of defects such as being used, and is an index for evaluating even more severe transport performance. Here, the relationship between the electrode pitch λ, the sum of the dielectric layer thickness A and the thickness B of the belt member, the value λ / (A + B) divided by the A + B value, and the above transport state is described.

  As can be seen from FIG. 16, under the condition of each electrode pitch, when the λ / (A + B) value is larger than 5, both the toner conveyance efficiency and the conveyance uniformity are obtained. That is, by setting the electrode pitch of the traveling wave generating electrode to be 5 times or more the thickness of the dielectric layer and the belt member existing above the electrode layer in the developer conveying member, good toner conveying performance can be obtained. It shows that you can.

  From the above, the electrode pitch λ, the development gap G, the thickness A of the dielectric layer, and the thickness B of the belt member are [0.5 <λ / G <2] and [5 × (A + B) <λ]. By setting so as to satisfy the relationship, it is possible to obtain an appropriate electrode pitch-development gap relationship that prevents edge thinning and suppresses fogging, and stable toner even when the electrode pitch is narrowed It becomes possible to maintain transportability.

-Contact angle-
As another means for improving the toner transportability, a method of reducing the adhesion force of the toner to the dielectric layer of the developer transport member or the surface of the belt member is also useful. By weakening the adhesion force of the toner, it is possible to transport the toner even in a lower electric field. However, the action to give the adhesion force with the toner includes the mirror image force due to the charge of the toner itself, the intermolecular force, the liquid crosslinking force, etc. Is the main element.

  Of these, focusing on the liquid cross-linking force, when the surface of the dielectric layer or the belt member has good hydrophilicity with respect to water, a thin water film is easily formed on the surface, which promotes the liquid cross-linking force. In particular, this action tends to increase in a high-humidity environment, and once the adhesion of the toner adhering to the dielectric layer or belt member is increased, the action of hindering the toner detachment action by the traveling wave electric field is strengthened. On the other hand, when the dielectric layer or the surface of the belt member is hydrophobic, the above-described action is weakened, the toner adhesion force is reduced, and the toner transportability can be improved.

  Thus, FIG. 17 shows the result of changing the material of the surface of the belt member and examining the relationship between the contact angle of the material with water and the transportability.

  However, in evaluating the transportability, the electrode pitch is 254 μm, the dielectric layer thickness A is 27.5 μm, the belt member thickness B is 30 μm ± 3 μm, and the normal environment (about 25 ° C./50% RH) Evaluation was performed in a wet environment (30 ° C./80% RH), and the degree of deterioration in transportability with respect to the normal environment was confirmed.

  From the results of FIG. 17, the transportability is good when the contact angle with water is 85 ° or more, but the tendency of the transportability to decrease is observed in other cases.

  Therefore, in the present invention, the contact angle with respect to water on the surface of the developer transport member on which the developer is transported or the contact angle with respect to water on the surface on which the developer layer of the belt member is formed is 85 ° or more. Stable toner conveyance can be performed without deteriorating the conveyance performance even in an environment.

  Further, as is apparent from the results of FIG. 17, the contact angle is increased by adding a fluorine-based substance to the surface of the developer transport member on which the developer is transported or the surface of the belt member on which the developer layer is formed. Thus, more stable toner transportability can be maintained.

-About fine particles-
In order to weaken the adhesion force of the toner, a method of weakening the intermolecular force acting on the toner is also effective. In general, in order to improve the fluidity of toner, by applying fine particles such as silica and titanium oxide on the surface as an external additive, apparently minute irregularities are formed on the surface, and the intermolecular force between the toners. It has been devised to weaken. This action can be applied to weaken the adhesion force action with the dielectric layer or belt member on the surface of the developer conveying member. However, the use of an excessively large amount of external additive is not practical due to the deterioration of its characteristics due to detachment or burying over time.

  Therefore, if the fine particles are dispersed in the dielectric layer or the belt member on the surface of the developer conveying member and a part thereof is exposed on the surface (see FIG. 13), the developer is caused by the surface unevenness due to the exposed fine particles. The action of weakening the force between the conveying member and the toner works, the adhesion force of the toner is reduced, and the conveying property can be improved. In this case, the amount of the external additive of the toner may be an amount necessary for improving the characteristics of the toner itself, and is more preferable without causing the above-described adverse effects.

  Further, when the fine particles are dispersed, if the particle size of the fine particles is too large, the surface roughness of the dielectric layer or the belt member on the surface of the developer conveying member becomes too large, which adversely affects the uniformity of toner conveyance.

  That is, when the degree of surface irregularities is too large with respect to the toner particle diameter, the conveyed toner may not be able to move smoothly due to the irregularities. In particular, when the toner particle size is about half of the toner particle size, the toner is caught on the unevenness of the toner conveying surface, and the toner is likely to be fixed (see FIG. 14). Further, in a system employing a belt member, it becomes difficult to clean the belt member, and it is difficult to always keep the surface of the belt member clean. In order to stably maintain the state in which the fine particles are exposed on the surface, that is, to prevent the fine particles from being detached due to use over time, a state in which about half of the size is buried is desirable. Therefore, in order to make the unevenness less than half the particle diameter of the toner, it is necessary to make the size of the dispersed fine particles smaller than the particle diameter of the toner.

  Therefore, in the present invention, the above-described problems can be solved by satisfying the relationship [r1 <r2] between the volume average particle diameter r1 of the fine particles and the volume average particle diameter r2 of the developer. Therefore, stable and uniform toner transportability can be maintained.

  Furthermore, in the case of dispersing the fine particles, if the dispersed fine particles are made of a fluorine-based substance, the hydrophobicity increases in addition to the above-described intermolecular force reducing effect due to the surface unevenness, and thus the above-described liquid crosslinking force reducing effect is added. In addition, options for the dielectric layer and belt member of the developer conveying member are widened, and a more appropriate material can be selected.

-Layer structure of dielectric layer and belt member on traveling wave generating electrode-
Fluorine-based material on the side that becomes the toner transport surface (the surface of the developer transport member on which the developer is transported or the surface of the belt member on which the developer layer is formed) In addition, although it is desirable to form a layer in which fine particles are dispersed, there are cases where the structure is not necessarily optimal in terms of other characteristics of these materials, for example, adhesiveness to other substances and strength.

  Therefore, when the developer conveying member is used alone, it is possible to take a measure such as selecting a material on the electrode layer side that can maintain good adhesion with the electrode layer. Can be prevented. When using a belt member, it is necessary to pay attention to the strength of the belt member. In the present invention, it is necessary to use a relatively thin belt member. By selecting a mechanically strong material as the base member, it is possible to maintain stable performance over time.

-About developer amount-
To achieve high image quality in image formation using toner, energy saving in the fixing process, reduction in running cost, and downsizing of the device by reducing the volume of the toner container, the toner is maintained while maintaining the required concentration. Therefore, it is necessary to develop a thin layer on the photosensitive member.

  However, it has been found that edge thinning tends to occur as described above under the condition of reducing toner consumption. Under the condition where the amount of developing toner is relatively large, the toner also enters the latent image edge portion of the photoreceptor with a certain probability and the latent image edge portion tends to become thicker. However, under the condition of a small amount of developing toner amount, the latent image It is difficult for toner to enter the edge portion, and the edge tends to be thin.

FIG. 18 shows the state of the edge thinning when the toner particle diameter and the developing toner amount are changed. From the results of FIG. 18, it is understood that if the volume average particle diameter of the toner is r2 (μm), edge thinning is likely to occur when the developer amount mo is r2 × 0.1 (mg / cm ² ) or less. However, as described above, such a phenomenon can be eliminated under the conditions of appropriately selecting the electrode pitch and the development gap as in the present invention. Therefore, it is possible to form a good image while enjoying the merits of the above-described thin layer development, and the developer amount mo (mg / cm ² ) and the volume average particle diameter r2 (μm) of the developer are expressed as [mo ≦ By combining the configurations of setting so as to satisfy the relationship of 0.1 × r2], it is possible to form a more suitable image.

  According to the developing device of the present invention, a developer conveying member having a plurality of traveling wave generating electrodes arranged at predetermined intervals on a substrate is used, and a traveling wave electric field formed by the developer conveying member is used. In a system in which development is carried out in a non-contact manner by carrying the developer toward the image carrier, the development gap G (mm) at the position where the developer carrying member and the image carrier are closest to each other, With respect to the arrangement pitch λ (mm) of the traveling wave generating electrodes and the dielectric thickness on the traveling wave generating electrode of the developer conveying member A (mm), [0.5 <λ / G <2] and [5 × A < In a configuration in which a belt member that covers the surface of the developer conveying member and moves on the surface in the developer conveying direction is added to the above method, the thickness of the belt member is set. As B (mm), [0.5 The development conditions are optimized by satisfying the relationship of λ / G <2] and [5 × (A + B) <λ], so that both edge prevention and fogging of the image are prevented. In addition, the developer conveying performance can be improved.

  According to the image forming apparatus of the present invention, since the developing device having the above-described features is provided, a high-quality image can be obtained while suppressing the consumption of the developer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Embodiment 1>
FIG. 1 is a diagram showing a configuration of an embodiment of an image forming apparatus provided with a developing device of the present invention.

  Inside the image forming apparatus X, a cylindrical photosensitive drum 1 as an image carrier is provided. A charging member 2, an exposure member 3, a developing device 4, a transfer member 5, a cleaning member 6, and a charge removal member 7 are arranged in this order around the photosensitive drum 1.

  Further, between the photosensitive drum 1 and the transfer member 5, a paper conveyance path for conveying a paper (PPC paper or the like) P as a recording medium is disposed. A fixing device 8 including a pair of upper and lower fixing members 81 and 81 is disposed on the downstream side of the photosensitive drum 1 when viewed from the conveyance direction of the sheet conveyance path.

  In the electrophotographic process, an electrostatic latent image corresponding to data captured from a document image or a host computer (not shown) is formed on the photosensitive drum 1, and the electrostatic latent image is developed (visualized) by the developing device 4. And the image is formed on the sheet P.

  The photoconductive drum 1 has a photoconductive layer 12 formed on a conductive substrate 11 and is rotatable from the charging member 2 according to the arrangement order of the members 3 to 7.

  First, the surface (photoconductive layer 12) of the photosensitive drum 1 is charged by the charging member 2 until it reaches a predetermined potential. The surface of the photosensitive drum 1 charged to a predetermined potential reaches the position of the exposure member 3 by the rotation of the photosensitive drum 1. The exposure member 3 is a writing unit, and writes an image on the surface of the photosensitive drum 1 that is charged by light such as laser light based on image information. As a result, an electrostatic latent image is formed on the photosensitive drum 1. The surface of the photosensitive drum 1 on which the electrostatic latent image is formed reaches the position of the developing device 4 by the rotation of the photosensitive drum 1.

  In the developing device 4, the electrostatic latent image on the surface of the photosensitive drum 1 is developed as a developer image by the developer (toner) T conveyed on the developer conveying member 41. The surface of the photosensitive drum 1 carrying the developer T reaches the position of the transfer member 5 by the rotation of the photosensitive drum 1.

  The transfer member 5 transfers the developer T on the surface of the photosensitive drum 1 onto the paper P. The developer image transferred from the photosensitive drum 1 onto the paper P is fixed on the paper P by the fixing device 8.

  The surface of the photosensitive drum 1 after the developer image is transferred reaches the position of the cleaning member 6 by the rotation of the photosensitive drum 1. The cleaning member 6 removes the developer T and paper dust remaining on the surface of the photosensitive drum 1. The surface of the photosensitive drum 1 cleaned by the cleaning member 6 reaches the position of the charge eliminating member 7 by the rotation of the photosensitive drum 1.

  The neutralizing member 7 removes the potential remaining on the surface of the photosensitive drum 1. One image formation is completed by the series of operations described above.

  As the photosensitive drum 1, for example, a photoconductive layer such as amorphous silicon (a-Si), selenium (Se), or an organic photo semiconductor (OPC) is formed on the outer peripheral surface of a conductive base (metal drum) made of aluminum or the like. Is formed in a thin film shape, but is not particularly limited.

  Examples of the charging member 2 include a conductive wire such as a tungsten wire, a metal shield plate, a corona charger made of a grid plate, a charging roller, a charging brush, and the like, but is not particularly limited.

  Examples of the exposure member 3 include a semiconductor laser and a light emitting diode, but are not particularly limited.

  Examples of the transfer member 5 include a corona transfer device, a transfer roller, and a transfer brush, but are not particularly limited.

  Examples of the cleaning member 6 include a cleaning blade, but are not particularly limited.

  The neutralization member 7 includes a neutralization lamp, but is not particularly limited.

-Developer-
Next, the developing device will be described.

  As shown in FIG. 2, the developing device 4 includes a casing 40, a developer transport member 41, a mixing paddle 42, a support member 43, a developer supply member 44, a developer collection member 45, and a developer layer thickness regulating member 46. Etc.

  The casing 40 accommodates the developer T therein, and supports members constituting the developing device 4 as necessary.

  The mixing paddle 42 is for mixing the developer T accommodated in the casing 40.

  The developer conveying member 41 is a substantially planar member that is slightly inclined to face the developing area of the photosensitive drum 1. In FIG. 2, the developer conveying member 41 is shown to be substantially planar, but the shape of the developer conveying member is not limited to this, and for example, a semicircular arc shape or a gently curved surface is formed. It does not matter if the shape is

  In addition, a support member 43 that holds the developer transport member 41 is provided on the casing 40 on the surface opposite to the surface that transports the developer T so that the developer transport member 41 can maintain the above arrangement. .

  A developer supply member 44 that supplies the developer T that is transported on the surface of the developer transport member 41 is provided at the lower end of the developer transport member 41. At the upper end portion of the developer conveying member 41, a developer collecting member 45 for accommodating unused developer T on the surface of the developer conveying member 41 in the casing 40 is provided. In this example, the developer recovery member 45 is in contact with the surface of the developer transport member 41 so as to be rotatable. However, the present invention is not limited to this. It may be.

  The developer supply member 44 is for supplying the developer T accommodated in the casing 40 to the developer transport member 41 and is provided in contact with the developer transport member 41 with a predetermined pressure. ing. The contact pressure between the developer supply member 44 and the developer transport member 41 may be a desired contact pressure provided by a spring or the like, and the elastic modulus of the developer supply member 44 and the developer transport member 41 is adjusted. Thus, the positional relationship between the two may be controlled. The developer supply member 44 is in contact with a developer layer thickness regulating member 46 for regulating the layer thickness of the developer layer formed on the surface thereof.

  The material of the developer supply member 44 is not particularly limited, and examples thereof include solid rubber such as silicone, urethane, EPDM (ethylene-propylene-diene-methylene copolymer), and foamed rubber. Further, conductivity may be imparted by adding carbon black or an ionic conductive agent (voltage application is also possible). Note that the voltage value applied to the developer supply member 44 and the developer transport member 41 may be set to an appropriate value, and a function of charging the developer T to the developer supply member 44 may be added. Further, for example, a thin blade (for example, the same material as that of the developer supply member 44 can be used) may be provided before the developer supply member 44 to charge the developer T.

  The developer collecting member 45 is for collecting the developer T that does not contribute to the development of the electrostatic latent image on the photosensitive drum 1 and returning it to the casing 40, and the material thereof is not particularly limited. For example, the same developer supply member 44 can be used.

  The support member 43 is for holding the developer conveying member 41 facing the developing area of the photosensitive drum 1, and the configuration thereof is not particularly limited. For example, ABS (acrylonitrile-butadiene-styrene: acrylonitrile butadiene styrene) resin can be used.

  The developer transport member 41 transports the developer T by the electric field curtain action. As shown in FIG. 3, the traveling wave generating electrode 41b for generating the electric field curtain action is formed on the base material 41a made of an insulating layer. A plurality of sets are sequentially arranged with four as one set. The surface side of the developer conveying member 41 is covered with a surface protection member 41c.

  Then, for example, a multiphase AC voltage as shown in FIG. 4 is applied to the traveling wave generating electrodes 41b... 41b from the multiphase AC power supply 47 so as to be parallel to the surface of the developer conveying member 41. An electric field curtain is generated in the direction, whereby the developer T is conveyed to the developing region by the electric field curtain action. Further, a bias voltage is applied to the traveling wave generating electrodes 41b.

  Here, specific details of the developer transport member 41 are characteristic portions of the present invention, and details thereof will be described later. For example, a base material 41a: polyimide (thickness: 25 μm) Further, the traveling wave generating electrode 41b: copper (thickness: 18 μm), the surface protective layer 41c: polyimide (thickness: 25 μm) can be exemplified.

  The traveling wave generating electrodes 41b are arranged in parallel to each other at intervals of about 50 dpi (dot per inch) to 300 dpi, that is, about 500 μm to 85 μm, and have a width of about 40 to 250 μm depending on the electrode pitch. It is a microelectrode.

  In this example, four microelectrodes 41b are made into one set, and a four-phase alternating voltage having a voltage waveform as shown in FIG. 4, for example, is applied to each set of traveling wave generating electrodes 41b. The traveling wave electric field is formed on the wave generating electrodes 41b... 41b. However, the present invention is not particularly limited to this, and a three-phase alternating voltage may be applied to a set of three microelectrodes. .

  The voltage waveform may be a sine wave or a trapezoidal wave, and the voltage value range is preferably about 100 V to 3 kV. The frequency range is preferably 100 Hz to 5 kHz. However, these voltage values and frequencies may be set appropriately depending on the shape of the traveling wave generating electrode 41b, the transport speed of the developer T, the material used for the developer T, and the like, and are not particularly limited.

<Embodiment 2>
As another example of the developing device of the present invention, the form shown in FIG. 5 can be mentioned. The developing device 100 shown in FIG. 5 is characterized in that an endless belt member (endless belt 101) is provided so as to cover the surface of the developer conveying member 41. The structure provided with such a belt member has the following advantages.

  First, in the case of the developing device 100 as shown in FIG. 2, the developer adheres on the developer conveying member 41 due to long-term use, and when this adheres, the developer conveying property may be adversely affected. Further, the surface of the developer conveying member 41 is provided with a surface protective layer 41c made of a dielectric material in order to protect the electrode member and prevent occurrence of leakage. The dielectric layer (surface protective layer 41c) is charged by the contact with the dielectric material, and the developer transport state is disturbed, and the potential difference from the photosensitive drum 1, that is, the development potential difference changes with time. The stable development action may be hindered. In order to prevent this, an endless belt member (endless belt 101) is provided, and this is rotated to clean the attached developer and remove the charge from the belt member, thereby solving the above-described problems.

  Hereinafter, this belt member-covered developing device will be described in detail with reference to FIG.

  5 includes a casing 103, a mixing paddle 104, a developer supply member 105, a developer recovery member 106, a developer layer thickness regulating member 107, a cleaning blade 108, a developer transport member 41, an endless belt 101, In addition, a support member 102 and the like are provided, and a multiphase AC power supply 47 and a development bias DC power supply 48 are connected to the developer transport member 41.

  The casing 103 accommodates the developer T inside and supports members constituting the developing device 100 as necessary. The mixing paddle 104 is for mixing the developer T accommodated in the casing 103. The developer collecting member 106 collects the toner that has not been used in the developing process in the casing 103 so that the toner is not scattered.

  As shown in FIG. 6, the developer conveying member 41 has a convex curved surface with a guide surface that guides the endless belt 101 facing the developing area of the photosensitive drum 1. The convex curved surface portion of the developer conveying member 41 is closest to the photosensitive drum 1.

  The developer conveying member 41 has the same structure as that shown in FIG. 3, and a traveling wave generating electrode 41b for generating an electric field curtain action is sequentially formed on a base material 41a made of an insulating layer. It is arranged continuously. The surface side of the developer conveying member 41 is covered with a surface protection member 41c. Then, for example, a multiphase AC voltage as shown in FIG. 4 is applied to the traveling wave generating electrodes 41b... 41b from the multiphase AC power supply 47 so as to be parallel to the surface of the developer conveying member 41. An electric field curtain is generated in the direction, whereby the developer T is conveyed to the developing region by the electric field curtain action.

  The endless belt 101 is provided on the surface of the developer conveying member 41 (the surface facing the photosensitive drum 1) so as to cover the surface in the circumferential direction.

  The endless belt 101 is stretched around the belt driving member 111, the driving auxiliary member 112, and the upper and lower belt guide members 113 and 114, and the belt driving member 111 rotates at a predetermined peripheral speed in the transport direction of the developer T. It is moved (turned).

  The developer layer is formed on the endless belt 101 by forming a developer layer controlled to a desired thickness and adhesion amount on the developer supply member 105 by the developer layer thickness regulating member 107, and then developing the developer layer. The developer layer on the supply member 105 is transferred onto the endless belt 101. Then, the endless belt 101 is moved (rotated), and the developer layer is transferred to a region where the traveling wave generating electrode 41b of the developer transport member 41 is present (see FIGS. 5 and 6). The developer T is conveyed to the development area by the traveling wave electric field that is formed.

  As a method of forming the developer layer on the endless belt 101, a method of directly forming the toner layer by bringing a developer layer thickness regulating member into contact with the endless belt 101 may be employed. Further, a developer is provided by bringing a sponge roller or the like into contact with the upstream side in the rotation direction of the endless belt 101 (the direction of arrow M in FIG. 5), or by providing a non-contact polygonal shape or a roughened rotation member. Supply assistance may be performed.

  In the developing device 100 of this example, as described above, the surface of the developer conveying member 41 is constantly renewed by rotating the endless belt 101 at a predetermined peripheral speed. The charging and the fixing of the developer T are prevented. As will be described later, the driving speed of the endless belt 101 is determined by the amount of developer on the endless belt 101, the amount of developer necessary on the photosensitive drum 1, and the peripheral speed of the photosensitive drum 1.

  The endless belt 101 is given a certain tension so as to be in close contact with the surface of the developer conveying member 41, and a traveling wave electric field (on the surface of the endless belt 101 formed by the traveling wave generating electrode 41b ( The electric field curtain) acts uniformly.

  The material and form of the endless belt 101 are features of the present invention, and details thereof will be described later. As an example, polyimide, PET (polyethylene terephthalate), polytetrafluoroethylene, polyfluorinated ethylene proprene, PTFE (polytetrafluoro) Examples thereof include organic materials such as ethylene), PVDF (polyvinylidene fluoride), polyamideimide, and nylon, and rubber materials such as silicone, isoprene, and butadiene. These belt member materials preferably have a high resistance (volume resistivity ρ: 1E + 9 to 14 Ω · cm, 100 V applied) in which an insulating or conductive agent is dispersed. Regarding conductivity imparting, an electron conduction type or an ionic conduction type can be used.

  As the belt driving member 111, a metal roller member such as SUS (stainless steel) or iron, or a member obtained by coating the surface with a member such as rubber, a film, or a sponge using this as a core metal is used.

  Furthermore, in this example, in order to make the endless belt 101 turn smoothly, a drive assisting member 112 is provided so as to contact the endless belt 101. The endless belt 101 is pushed by the drive assisting member 112 so that the frictional force with the belt driving member 111 is increased, and the contact property with the belt driving member 111 is high, so that a high driving force can be obtained. It has a structure. Furthermore, even when the peripheral length of the endless belt 101 varies due to production variations, usage over time, or usage environment, the drive assisting member 112 can provide an effect of stably maintaining the contact state with the developer conveying member 41.

  As the driving assisting member 112, like the belt driving member 111, a metal roller member such as SUS or iron, or a member obtained by coating the surface with a member such as rubber, a film, or a sponge using the same as a metal core. it can. Further, the shape of the drive assisting member 112 may be not only a roller shape but also a plate shape or a square shape.

  Further, the driving assisting member 112 may be provided with a pressing means (not shown) for pressing and contacting the belt driving member 111. As the pressurizing means, for example, a plate spring, a coil spring or the like that can apply a pressing force can be exemplified.

  Examples of the rotation mechanism of the drive assisting member 112 include a driven rotation mechanism that is brought into contact with the endless belt 101, and a connection drive mechanism that is connected to a drive source of the belt drive member 111 by a gear or pulley and a belt member. Further, the drive assisting member 112 may be provided with another drive source, or the potential charged on the surface of the endless belt 101 can be eliminated by electrically grounding the drive assisting member 112.

  Further, in this example, a cleaning blade 108 that contacts the belt driving member 111 via the endless belt 101 is provided as a cleaning member for removing the developer T adhering to the endless belt 101. The cleaning blade 108 is fixed to a part of the casing 103. Examples of the material of the cleaning blade 108 include SUS, nickel-coated iron, urethane, or silicon rubber.

  The cleaning blade 108 scrapes off the developer T remaining on the endless belt 101, cleans the surface of the endless belt 101, and returns the developer T to the developer accumulation portion 103 a of the casing 103. In the structure of FIG. 5, the endless belt 101 side and the developer accumulation unit 103a are disposed so that the developer T does not adhere to the endless belt 101 existing in the region between the cleaning blade 108 and the developer supply member 105. A partition wall member 109 is provided to separate the endless belt 101, and the endless belt 101 can be cleaned more effectively.

  A developer supply member 105 made up of a roller member that supplies the developer T to the endless belt 101 is provided at the lower end of the developer transport member 41. Further, a developer collecting member 106 formed of a roller member for collecting the developer T on the surface of the endless belt 101 in the casing 103 is provided at the upper end portion of the developer conveying member 41. In this example, the developer collecting member 106 is configured to be in contact with the surface of the endless belt 101 so as to be rotatable. However, the present invention is not limited to this, and the developer collecting member 106 is not contacted or rotated. There may be.

  The developer supply member 105 is for supplying the developer T accommodated in the casing 103 onto the endless belt 101 and supplying it to the developing region, and abuts against the endless belt 101 with a predetermined contact pressure. It is provided in the state. The pressure contact force between the developer supply member 105 and the endless belt 101 (belt guide member 114) is applied by a spring or the like. The developer supply member 105 is in contact with a developer layer thickness regulating member 107 for regulating the layer thickness of the developer layer formed on the surface thereof.

  The material of the developer supply member 105 is not particularly limited, and examples thereof include solid rubber such as silicone, urethane, EPDM (ethylene-propylene-diene-methylene copolymer), and foamed rubber. Further, conductivity may be imparted by adding carbon black or an ionic conductive agent (voltage application is also possible).

  The positional relationship between the developer supply member 105 and the endless belt 101 (belt guide member 114) may be adjusted by adjusting the elastic modulus. Furthermore, the voltage applied to the developer supply member 105 may be set to an appropriate value, and a function for charging the developer T may be added to the developer supply member 105. Alternatively, for example, a thin plate-like blade (the same material as the developer supplying unit can be used) may be provided in the front stage of the developer supplying member 105 to charge the developer T.

  The developer recovery member 106 is for recovering the developer T that does not contribute to the development of the electrostatic latent image on the photosensitive drum 1 and returning it to the casing 103. The material of the developer recovery member 106 is not particularly limited. For example, the same developer supply member 105 can be used.

  The support member 102 is for holding the developer conveying member 41 facing the developing area of the photosensitive drum 1, and the configuration thereof is not particularly limited. As the material, for example, ABS (acrylonitrile-butadiene-styrene: acrylonitrile butadiene styrene) resin can be used.

  Hereinafter, specific examples of the present invention will be described. In each example, various conditions were set using the image forming apparatus X to which the developing device 4 or the developing device 100 described above was applied.

<Example 1>
In Example 1, three types of FPCs having an electrode pitch λ of the developer conveying member of 508 μm, 254 μm, and 127 μm were used. The electrode width W was set to 1/2 of the electrode pitch λ.

  The amplitude of the alternating voltage for forming the traveling wave electric field was set to a condition that can be maximized in a range where no leakage occurs, and was set to ± 900 V, ± 450 V, and ± 225 V, respectively.

  Further, the charging voltage Vo and exposure potential VL of the photosensitive member (photosensitive drum), and the central value Vd of the applied voltage of the developer conveying member corresponding to the developing potential depend on the characteristics of the toner used, the electrode pitch, and other conditions. However, it was set so as to obtain a desired maximum development amount. VL was set to about -30 to -50V, and Vo was selected in the range of -500 to -1000V. However, in the comparison between the conditions with different electrode pitches, the value of Vo-VL was compared under the same conditions. This is because the electric field strength in the lateral direction at the latent image edge is greatly affected by the Vo-VL value.

Further, as the developer, a negatively charged toner having a volume average particle size of 4.3 μm, 5.7 μm, and 7.5 μm was used. The specific charge amount of the toner is in the range of −5 to −70 μC / g depending on the particle diameter, and the toner supply amount is adjusted so that the developing amount on the photoreceptor is about 0.4 mg / cm ² .

  Under the above conditions, with respect to the value [λ / G value] obtained by changing the development gap G and dividing the electrode pitch λ (μm) by the development gap G (μm), the degree of edge thinning and the state of fogging Evaluated. For the evaluation of edge thinning, a 5 mm square patch pattern was developed on the photosensitive member, and the amount of change in the width with respect to a predetermined width (the width of the writing data) was evaluated.

  As an evaluation standard for edge thinning, a toner image formed on an OPC (using OPC as a photoconductor) is collected with a mending tape or the like, and a 5 mm square patch shape is clearly visible (approximately 0). .2 to 0.3 mm or more) is “x”, and when the degree of thinness is slight, the amount of change of the width with respect to the predetermined width is measured with an optical microscope. ”And below, it was evaluated as“ ◯ ”or“ ◎ ”.

  For evaluation of fog, the toner adhering to the non-image area on the OPC was peeled off with a mending tape, and this was measured with a reflection densitometer (model 310 manufactured by X-Rite). The evaluation was “x” for 2 or more, “Δ” for 0.15 or more, and “◯” or “◎” for less than that.

  FIG. 15 shows the result of evaluating the image forming state with respect to the λ / G value by the above method. From the result of FIG. 15, when the range of λ / G value showing a good state with respect to both the edge thinness and the fog is seen, it is good when the range is larger than about 0.5 and smaller than 2. It can be seen that the image forming conditions are satisfied. That is, it is shown that the edge gap can be prevented and the fog can be suppressed by making the developing gap G half or twice of the electrode pitch λ.

  Further, as a result of examining the toner conveyance performance with respect to the relationship between the dielectric layer thickness A (μm) on the developer conveyance member and the thickness B (μm) of the belt member (endless belt) with respect to the electrode pitch λ (μm). Is shown in FIG.

  Here, as conditions for changing the thickness of the dielectric layer (surface protective layer), the dielectric layer is formed of a polyimide film of 12.5 μm and an adhesive layer of 15 μm, and the total thickness is 27.5 μm, The thickness of the polyimide film is 25 μm, the layer thickness is 40 μm, and the polyimide ink is printed on the electrode, which is baked at about 400 ° C. and directly formed without the adhesive layer. Three types having a thickness of 12 μm were used (see FIGS. 11A and 11B). Further, as the belt member, a polyimide film tube having a thickness of 12.5 μm, 19 μm, 31 μm, 60 μm, and 150 μm was used (see FIG. 11C).

  The relative dielectric constant of the polyimide film and tube used in this example was about 1.5 to 2.5. In the measurement, a 4284A precision LCR meter manufactured by Agilent Technologies was used, and the measurement was performed at a frequency of 500 to 2000 Hz as a condition close to the traveling wave voltage frequency.

  These dielectric layers and belt members were combined, and the relationship between the A + B value (B = 0 when no belt member was used) with respect to the electrode pitch λ was examined.

  The applied voltage condition for forming the traveling wave electric field, the condition of the toner to be used, and the like are the same as those in the study of FIG. 15, and the development gap G is λ / The toner conveyance efficiency was evaluated under the condition of G = 1. However, the toner transport efficiency depends on the phenomenon that the toner is not transported by the traveling wave electric field on the developer transport member, or in the system using the belt member, the supplied toner formed on the belt member. It was evaluated whether or not it can be conveyed by a traveling wave electric field with almost no excess.

  Further, as another evaluation of the conveyance performance, the uniformity of the toner conveyance state was evaluated. When the toner transport electric field works satisfactorily, toner behavior similarly occurs in the longitudinal direction (direction perpendicular to the toner transport direction) with respect to the action of the traveling wave electric field, resulting in a uniform transport state.

  However, when the transport electric field is insufficient, there may be a phenomenon that even if the toner moves in an arbitrary place, the transport is not started in another place. That is, in such a case, the space density of the toner cloud when the toner is being conveyed is non-uniform, and if development is performed on the photoconductor in such a state, the development becomes a streak-like or spotted uneven state. This is an investigation of the occurrence of defects such as being used, and is an index for evaluating even more severe transport performance.

  The evaluation standard of the conveyance efficiency is “◯” or “◎” when the toner hardly remains on the dielectric layer or the belt member of the developer conveying member, and “△” when the toner remains slightly visually. In the case where almost no toner is transported, “X” is given.

  Next, the relationship between the electrode pitch λ, the sum of the dielectric layer thickness A and the thickness B of the belt member, the value λ / (A + B) divided by the A + B value, and the above transport state will be described.

  As shown in FIG. 16, under the condition of each electrode pitch λ, when the λ / (A + B) value is larger than 5, both the transport efficiency and the transport uniformity are good. This means that a good toner conveying performance can be obtained by setting the electrode pitch λ to be 5 times or more the thickness of the dielectric layer and the belt member existing above the electrode layer in the developer conveying member. Show.

  Accordingly, the relationship of [0.5 <λ / G <2] and [5 × (A + B) <λ] is satisfied with respect to the electrode pitch λ, the development gap G, the dielectric layer thickness A, and the belt member thickness B. Thus, it is possible to obtain an appropriate electrode pitch and development gap relationship that prevents edge thinning and suppresses fogging. Furthermore, stable toner transportability can be maintained even when the electrode pitch is narrowed.

  That is, with respect to edge thinning, a traveling wave electric field is generated by reducing the development gap G with respect to the electrode pitch λ, in other words, by increasing the value to 0.5 or more in the direction of increasing λ / G. The influence of the individual electrodes acts in the vicinity of the photosensitive member, and an effect of pushing the toner into the latent image edge portion is created, so that the edge thinning can be reduced.

  On the other hand, from the viewpoint of prevention of background fogging, it becomes worse when the development gap is narrowed too much. Therefore, by making the λ / G value smaller than 2, the influence of individual electrodes on the non-image area is weakened, and fogging suppression action is achieved. Can be increased. Furthermore, from the viewpoint of stabilizing the toner conveyance performance, when the dielectric layer thickness of the developer conveyance member is A and the thickness of the belt member is B with respect to the electrode pitch λ, the traveling wave electric field on the toner conveyance surface is From the viewpoint of ensuring, this can be achieved by setting the electrode pitch λ to be larger than 5 times the value of A + B.

<Example 2>
In Example 2, the material of the surface of the belt member was changed, and the relationship between the contact angle of the material with water and the transportability was examined. The result is shown in FIG. In the evaluation of the conveyance performance, the electrode pitch λ is 254 μm, the dielectric layer thickness A is 27.5 μm, the belt member thickness B is 30 μm ± 3 μm, and the normal environment (about 25 ° C./50% RH) Evaluation was performed in a wet environment (30 ° C./80% RH), and the degree of deterioration in transportability with respect to the normal environment was confirmed.

  The evaluation criteria for the conveyance performance are the same as those in the first embodiment. Also in this case, the evaluation was performed under the condition that the development gap G is λ / G = 1 with respect to the electrode pitch λ (here, since λ = 254 μm, the development gap is about 250 μm). From the results shown in FIG. 17, the transportability is good under the condition where the contact angle is 85 ° or more.

  Therefore, by setting the contact angle between the belt member surface and water to 85 ° or more, stable toner conveyance can be performed without deteriorating the conveyance performance even in a high humidity environment.

  Further, as apparent from FIG. 17, a material containing a fluorine-based material has a large contact angle and can maintain more stable toner transportability. With regard to the PVDF belt member, it has a conductivity, a contact angle is small, and the conveyance performance is not excellent, but other than that, a fluorine-based material shows preferable characteristics.

  Further, in Example 2, not only a single material but also a polyimide coated with PFA showed good characteristics. Here, a 19 μm polyimide belt member coated with a PFA coating of about 10 μm was used.

  Here, the belt member used in the present invention needs to be very thin, and is desirably a high-strength material. By adopting such a multilayer structure, it is possible to achieve both excellent characteristics in terms of polyimide strength and the water repellent effect of PFA, which is more preferable.

  In addition, even in a system that does not use a belt member, it is preferable because options for selecting a material constituting the FPC are expanded. At present, what is widely distributed as FPC is mainly based on polyimide or PET. Although the PET type is relatively low in cost, the hydrophobicity of PET is not so high. However, it is possible to realize an FPC having a water repellent effect at low cost by applying a PFA coat or the like to the surface. Further, since the same material is used for manufacturing the FPC itself, it is preferable that distortion due to a difference in adhesiveness or shrinkage does not occur.

<Example 3>
As means for forming minute irregularities on the toner conveying surface, silica particles or titanium oxide particles (20 as external additives for toner) in a resin solution such as polyimide, nylon, PVDF, and PTFE that can be used as a belt member material. A belt member was manufactured using a dispersion in which 1 to 10 wt% was dispersed. In such a belt member, a part of the aforementioned additive fine particles is exposed on the surface, and minute irregularities are formed on the surface. With the size of the additive fine particles described above, the degree of unevenness is about 0.1 μm or less.

  By using such a belt member, the minute unevenness on the surface of the belt member gives an effect of reducing the intermolecular force between the toner and the belt member, and a more stable toner conveyance state can be secured.

  It is also preferable to add fluorine-based fine particles as the fine particles to be added. Examples of the fluorine-based fine particles include PTFE fine particles. The size is preferably the same as described above. By adopting such a form, not only the above-described intermolecular force reduction effect but also the above-mentioned water repellency effect is imparted, and the liquid cross-linking ability is reduced, so that stable toner conveyance can be performed even in a high humidity environment. Moreover, what performed the hydrophobization process of the above-mentioned silica particle or titanium oxide particle may be used.

  Further, when fine particles having the same particle diameter as the toner particle are used as the additive fine particles, very large irregularities are formed as shown in FIG. The size of the unevenness is about several μm, and the toner is caught in the middle of the conveyance, which disturbs the stable toner conveyance. For this reason, the size of the fine particles to be added is less than the particle diameter of the toner, preferably about 1/10 or less.

<Example 4>
In order to improve image quality in image formation using toner, save energy in the fixing process, reduce running costs, and reduce the size of the device by reducing the volume of the toner container, the toner concentration is maintained while maintaining the required concentration. It is necessary to develop a thin layer on the photoconductor, that is, a condition for reducing consumption.

  However, edge thinning may occur under such conditions. Under a relatively large amount of developing toner, the toner enters the latent image edge portion of the photoconductor with a certain probability and the latent image edge portion tends to become thick. However, under a small amount of developing amount, the latent image It is difficult for toner to enter the edge portion, and the edge tends to be thin.

  FIG. 18 shows the state of edge thinning when the toner particle size and the developing toner amount are changed. A toner having a volume average particle size of 7.5 μm, 5.7 μm, and 4.3 μm is used. The amount of toner on the belt member and the moving speed of the belt member are adjusted, and the amount of development on the photosensitive member is adjusted. Changed. Further, the electrode pitch λ was set to 254 μm and the development gap G was set to 1 mm, that is, λ / G was set to about 0.25, which was outside the scope of the present invention.

From the results shown in FIG. 18, edge thinning is unlikely to occur under conditions where the amount of developing toner is relatively large, but edge thinning tends to occur as the thin layer development conditions are reached. Further, it can be seen from the results of FIG. 18 that, when the volume average particle diameter of the toner is r2 (μm), it easily occurs when the development amount mo is r2 × 0.1 (mg / cm ² ) or less.

  However, such a phenomenon is eliminated under the conditions for appropriately selecting the electrode pitch λ and the development gap G as in the first embodiment.

  Therefore, it is possible to form a good image while enjoying the advantages of the above thin layer development, and it is possible to form a more suitable image by combining with the configuration of this example.

  The present invention relates to a developing device for developing an electrostatic latent image formed on an elephant carrier (photosensitive drum) with a developer, and an image forming apparatus including the developing device, and in particular, transports the developer using a traveling wave electric field. Therefore, it can be effectively used for a developing device and an image forming apparatus that use a mechanism (electric field curtain).

1 is a diagram schematically illustrating a configuration of an embodiment of an image forming apparatus of the present invention. It is a figure which shows typically the structure of embodiment of the image development apparatus of this invention. It is a figure which shows typically the structure of a developer conveyance member. It is a figure which shows the waveform of the alternating voltage of 4 phases applied to a developer conveyance member. It is a figure which shows typically the structure of another embodiment of the image development apparatus of this invention. FIG. 6 is an enlarged view of a Z portion in FIG. 5. It is explanatory drawing of the edge effect of the image development system using a toner. FIG. 10 is an explanatory diagram of a difference in development state due to an edge effect when toner amounts are different. It is explanatory drawing of the edge thinning reduction effect | action at the time of changing a development gap. It is explanatory drawing of the fog generating effect | action when the electrode pitch in a developer conveyance member differs. It is a figure which shows typically the structure of the dielectric material layer on a developing agent conveyance member. FIG. 6 is an explanatory diagram of quality of toner transportability. It is explanatory drawing of the state which disperse | distributed microparticles | fine-particles in a dielectric material layer and a belt member. It is explanatory drawing which shows the malfunction when the microparticles | fine-particles disperse | distributed in a dielectric material layer and a belt member are too large. It is a figure which shows the result of having evaluated the image formation state at the time of changing a development gap using the developer conveyance member which has three types of electrode pitches. FIG. 10 is a diagram illustrating a result of evaluating toner conveyance performance with respect to a relationship between a dielectric layer thickness on a developer conveyance member and a belt member thickness B with respect to an electrode pitch. It is a figure which shows the result of having changed the material of the surface of a belt member, and having evaluated the relationship between the contact angle with the water of the material, and conveyance property. It is a figure which shows the result of having evaluated the state of the edge thinning at the time of changing a toner particle size and a developing toner amount.

Explanation of symbols

X Image forming device 1 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 11 Conductive substrate 12 Photoconductive layer 2 Charging member 3 Exposure member 4 Developing apparatus 40 Casing 41 Developer conveyance member 41a Base material 41b Traveling wave generating electrode 41c Surface protective layer (dielectric)
42 Mixing Paddle 43 Support Member 44 Developer Supply Member 45 Developer Recovery Member 46 Developer Layer Thickness Restricting Member 47 Multiphase AC Power Supply 48 Development Bias DC Power Supply 5 Transfer Member 6 Cleaning Member 7 Charge Removal Member 8 Fixing Device 100 Developing Device 101 Endless Belt (belt member)
DESCRIPTION OF SYMBOLS 111 Belt drive member 112 Drive assist member 113,114 Belt guide member 102 Support member 103 Casing 104 Mixing paddle 105 Developer supply member 106 Developer collection member 107 Developer layer thickness control member 108 Cleaning blade P Paper T Developer (toner)

Claims (10)

A developing device for developing an electrostatic latent image formed on a surface of an image carrier with a developer, and having a plurality of traveling wave generating electrodes arranged on a substrate at predetermined intervals, and In a developing device including a developer transport member that transports the developer toward the image carrier by a traveling wave electric field formed by applying a plurality of alternating voltages having different phases to the traveling wave generating electrode.
The developer gap at the position where the developer carrying member and the image carrier are closest to each other is G (mm), the arrangement pitch of traveling wave generating electrodes of the developer carrying member is λ (mm), and the developer carrying member A developing device satisfying the relations [0.5 <λ / G <2] and [5 × A <λ] where the dielectric thickness on the traveling wave generating electrode is A (mm). A developing device for developing an electrostatic latent image formed on a surface of an image carrier with a developer, and having a plurality of traveling wave generating electrodes arranged on a substrate at predetermined intervals, and A developer conveying member that conveys the developer toward the image carrier by a traveling wave electric field formed by applying a plurality of alternating voltages having different phases to the traveling wave generating electrode; and A belt member that covers the surface and moves on the surface in the developer transport direction, forms a developer layer on the belt member, and a traveling wave electric field is formed on the developer transport member by the developer transport member. In a developing device configured to be transferred to an area
The developing gap at the position where the belt member and the image carrier are closest to each other is G (mm), the arrangement pitch of the traveling wave generating electrodes of the developer conveying member is λ (mm), and the traveling of the developer conveying member When the dielectric thickness on the wave generating electrode is A (mm) and the thickness of the belt member is B (mm), [0.5 <λ / G <2] and [5 × (A + B) <λ] A developing device characterized by satisfying the above.   The contact angle with respect to water of the surface on which the developer of the developer transport member is transported or the contact angle with respect to water of the surface of the belt member on which the developer layer is formed is 85 ° or more. Item 3. The developing device according to Item 1 or 2.   4. The developing device according to claim 3, wherein a surface of the developer conveying member on which the developer is conveyed or a surface on which the developer layer of the belt member is formed contains a fluorine-based substance. .   The fine particles are dispersed in the dielectric layer on the traveling wave generating electrode of the developer conveying member or the belt member, and some of the fine particles are exposed on the surface. Item 5. The developing device according to any one of Items 1 to 4.   6. The developing device according to claim 5, wherein a relation of [r1 <r2] is satisfied, where r1 is a volume average particle diameter of the fine particles and r2 is a volume average particle diameter of the developer.   The developing device according to claim 5, wherein the fine particles are a fluorine-based substance.   The development according to claim 1, wherein the dielectric layer on the traveling wave generating electrode of the developer conveying member or the belt member is made of at least two layers of material. apparatus. When the developer amount developed on the image bearing member is mo (mg / cm ² ) and the volume average particle diameter of the developer is r2 (μm), the relationship of [mo ≦ 0.1 × r2] is satisfied. 9. The developing device according to claim 1, wherein An image forming apparatus comprising: an image forming unit that forms an image based on image data; and the developing device according to claim 1.

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