JP2004264499A - Image forming method and image forming apparatus used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method by which filming is reliably prevented without using a toner with an abrasive external additive or a special device for polishing a photoreceptor, and to provide an image forming apparatus suitable for carrying out the method. <P>SOLUTION: A first image forming method related to this invention includes an image forming process in which at least electrifying, exposing, developing, transferring and cleaning steps are carried out in this order, and after the end of the developing step and before new start of an electrifying step, a polishing process is included in which a second electrifying step of uniformly electrifying a photoreceptor surface, a step of shifting a magnetic carrier to the photoreceptor surface, and a step of polishing the photoreceptor surface while removing the carrier with a cleaning means are carried out in this order. For example, the photoreceptor surface is polished by setting the difference between effective potential difference ΔVep in the polishing process and effective potential difference ΔVei in the image forming process within a prescribed range. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００６３】
表１中、「磁性キャリアの移行量」は、上記一連の画像形成処理を１０００サイクル繰り返したときの移行量（ｇ）を示す。“評価結果”の欄の「―」は、上記一連の画像形成装置を３０万サイクル繰り返した後であっても、静電潜像担持体（感光体）の表面にて傷やフィルミングの発生が確認されなかったことを示す。また、同欄の「…万枚で傷が発生」または「…万枚でフィルミングが発生」とは、上記一連の画像形成装置を…万サイクル繰り返したときに、静電潜像担持体の表面にて傷の発生、またはフィルミングの発生が確認されたことを示す。
【００６４】
表２より明らかなように、本発明の第２の画像形成方法により画像形成を行った実施例では、上記一連の画像形成処理を３０万サイクルという、極めて多くの回数繰り返した後であっても、静電潜像担持体の表面にて傷やフィルミングが発生するという不具合を生じることがなかった。
これに対し、比較例では、｜ΔＶｅｐ｜−｜ΔＶｅｉ｜が小さすぎる場合に、静電潜像担持体の表面にフィルミングが発生するという問題が発生して、逆に、｜ΔＶｅｐ｜−｜ΔＶｅｉ｜が大きすぎる場合に、静電潜像担持体の表面に傷がつくという問題が発生した。この原因は、前者の場合は磁性キャリアの移行量が少なくなりすぎたこと、後者の場合は磁性キャリアの移行量が多くなりすぎたことにあるものと推測される。
【００６５】
〔第２の画像形成方法による実施例〕
本発明に係る第２の画像形成方法を使用して、実機による画像形成試験を行った。試験には、トナーと磁性キャリアとを含む２成分系の現像剤を使用した。
かかる現像剤のうち、使用したトナーおよびトナーと磁性キャリアとの混合割合については「第１の画像形成方法による実施例」と同様である。
磁性キャリアには、フェライト粒子の表面にシリコーン樹脂をコーティングしたコート型キャリアを使用した。この磁性キャリアは、重量平均粒径が６０μｍであって、目開き３０μｍのメッシュを通過したものと、当該メッシュを通過しなかったものとを含んでおり、当該メッシュを通過しなかったものについての飽和磁化は６０ｅｍｕ／ｇであった。目開き３０μｍのメッシュを通過したものについての飽和磁化と、その含有割合は、実施例および比較例毎に適宜調整した。
なお、飽和磁化の測定は、理研電子（株）製の磁気測定試験機「ＢＨＵ−６０」を使用して、３，０００Ｏｅの磁場を印加した条件で測定した。
【００６６】
（実施例３）
画像形成試験には、実施例１の場合と同様に、電子写真複写機〔前出の「ＫＭ−５５３０」の改造機〕を画像形成装置として使用した。静電潜像担持体（感光体）表面の周速、現像剤担持体（現像スリーブ）と感光体との周速比（Ｓ／Ｄ）、現像スリーブの穂切り高さ、感光体−現像スリーブ間距離、現像スリーブの主極の磁力およびその位置、ならびに試験時の環境条件は、いずれも「第１の画像形成方法による実施例」と同じ条件とした。
また、現像スリーブのバイアス電圧（現像バイアス電圧）は＋６００Ｖに、感光体の明電位は＋１５０Ｖに、暗電位は＋８００Ｖに、それぞれ設定した。
【００６７】
実施例３において、上記２成分系現像剤の磁性キャリアのうち、目開き３０μｍのメッシュを通過したものについては、その飽和磁化を４５ｅｍｕ／ｇに、当該メッシュを通過した磁性キャリアの全磁性キャリア中での含有割合を２０重量％に、それぞれ調整した。
上記の画像形成装置および２成分系現像剤を使用して、上記の条件にて、Ａ４サイズの黒文字原稿（黒比率６％）の画像形成処理（複写処理）を３０万サイクル繰り返した。
【００６８】
（実施例４および比較例３〜６）
２成分系現像剤の磁性キャリアのうち、目開き３０μｍのメッシュを通過したものとして、飽和磁化が５５ｅｍｕ／ｇ（実施例２および比較例４）、４５ｅｍｕ／ｇ（比較例３）、４４ｅｍｕ／ｇ（比較例５）または５６ｅｍｕ／ｇ（比較例６）であるものを使用し、かつ当該メッシュを通過した磁性キャリアの全磁性キャリア中での含有割合を３重量％（実施例２および比較例６）、２１重量％（比較例３）、２重量％（比較例４）または２０重量％（比較例５）となるように調節した。
かかる２成分系現像剤を使用したほかは、実施例３と同様にして画像形成処理（複写処理）を３０万サイクル繰り返した。
【００６９】
（研磨効果の評価）
上記実施例および比較例では、帯電、露光、現像、転写およびクリーニングの各工程を含む一連の画像形成処理を１０００サイクル繰り返す毎に、回収トナー中に混入している磁性キャリアの量と、２成分現像剤中から消費された磁性キャリアの量とを測定した。また、静電潜像担持体の表面状態やフィルミングの有無を目視で観察することにより、磁性キャリアによる静電潜像担持体（感光体）の研磨効果を評価した。
なお、回収トナー中の磁性キャリアの混入量をもとにして、磁性キャリアの静電潜像担持体表面への移行量（ｇ）を算出した。
【００７０】
以上の結果を表２に示す。
【００７１】
【表２】

【００７２】
表２中、「低飽和磁化・小粒径磁性キャリア」とは、目開き３０μｍのメッシュを通過した磁性キャリアのことを示す。「磁性キャリアの移行量」は、上記一連の画像形成処理を１０００サイクル繰り返したときの移行量（ｇ）を示す。“評価結果”の欄の「―」は、上記一連の画像形成装置を３０万サイクル繰り返した後であっても、静電潜像担持体（感光体）の表面にて傷やフィルミングの発生が確認されなかったことを示す。また、同欄の「…万枚で傷発生」または「…万枚でフィルミング発生」とは、上記一連の画像形成装置を…万サイクル繰り返したときに、静電潜像担持体の表面にて傷の発生、またはフィルミングの発生が確認されたことを示す。
【００７３】
表２より明らかなように、飽和磁化と粒径とが所定の範囲に設定された低飽和磁化・小粒径磁性キャリアを所定の割合で含有する２成分系現像剤を用いて、本発明の第２の画像形成方法により画像形成を行った実施例では、上記一連の画像形成処理を３０万サイクルという、極めて多くの回数繰り返した後であっても、静電潜像担持体の表面にて傷やフィルミングが発生するという不具合を生じることがなかった。
【００７４】
これに対し、比較例では、低飽和磁化・小粒径磁性キャリアの飽和磁化が低すぎまたはその含有割合が多すぎる場合に、静電潜像担持体の表面に傷がつくという問題が発生して、逆に、低飽和磁化・小粒径磁性キャリアの飽和磁化が高すぎまたはその含有割合が少なすぎる場合に、静電潜像担持体の表面にフィルミングが発生した。この原因は、前者の場合は磁性キャリアの移行量が多くなりすぎたこと、後者の場合は磁性キャリアの移行量が少なくなりすぎたことにあるものと推測される。
【図面の簡単な説明】
【図１】画像形成装置の一例を示す模式図である。
【図２】静電潜像担持体の表面電位の推移と、現像剤担持体の表面に印加される現像バイアス電圧との関係を示す説明図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming method capable of efficiently preventing filming using a two-component developer, and an image forming apparatus used in the image forming method.
[0002]
[Prior art]
In electrophotographic image formation, the quality of a formed image is degraded due to so-called filming in which toner and components such as wax mixed in toner particles adhere to the surface of an electrostatic latent image carrier (photoconductor). There is a problem.
Therefore, in the inventions described in Patent Documents 1 and 2, abrasive particles such as titanium oxide and alumina are externally added (externally added) to toner particles of a developer, and the photoreceptor surface is polished with the fine particles. Trying to prevent ming.
However, there is a problem that the abrasive fine particles themselves cause a new filming by migrating and depositing on the photoreceptor surface. Further, there is a possibility that the charging of the toner and the carrier may be hindered.
[0003]
On the other hand, Patent Literature 3 discloses a polishing blade (polishing device) for polishing and removing wax and the like adhering to the surface of a photoconductor separately from a cleaning blade for removing toner remaining on the surface of the photoconductor. An electrophotographic device comprising:
However, in recent years, downsizing of the image forming apparatus has been demanded, and there is a space problem in attaching the above-described polishing apparatus. In addition, the above-mentioned polishing apparatus is disadvantageous in reducing the cost of the image forming apparatus.
[0004]
[Patent Document 1]
JP-A-8-82952 (Claim 1, Paragraph [0013])
[Patent Document 2]
JP-A-7-92720 (Claim 1, Paragraph [0009])
[Patent Document 3]
JP-A-5-323833 (paragraph [0007], paragraph [0008])
[0005]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming method capable of reliably preventing the occurrence of filming without using a toner to which abrasive fine particles are externally added or a special device for polishing the surface of an electrostatic latent image carrier. And to provide an image forming apparatus suitable for the implementation.
[0006]
Means for Solving the Problems and Effects of the Invention
In order to solve the above-mentioned problems, the present inventors have (i) forcedly or (ii) spontaneously charged a part of the magnetic carrier contained in the two-component developer. When the magnetic carrier is transferred to the surface of the image carrier and removed by the same cleaning means for removing the toner remaining on the surface of the electrostatic latent image carrier, the electrostatic latent image carrier is removed at the same time as the removal processing. The surface of the electrostatic latent image carrier can be polished without using a toner to which abrasive particles are externally added or a special device for polishing the surface of the electrostatic latent image carrier. The present inventors have found a completely new fact that it is possible to maintain the clean state of the present invention, and have completed the present invention.
[0007]
(First image forming method)
The first image forming method according to the present invention includes:
At least a charging step of uniformly charging the surface of the electrostatic latent image carrier, an exposure step of exposing the surface of the electrostatic latent image carrier to form an electrostatic latent image, and a surface of the developer carrier A developing step of visualizing the electrostatic latent image with the toner carried on the toner, a transfer step of transferring the toner image formed on the electrostatic latent image carrier by the visualization onto a transfer-receiving body, A cleaning step of bringing a cleaning unit into contact with the surface of the latent electrostatic image bearing member, and an image forming process step of performing an image forming process step in this order,
A second charging step of uniformly charging the surface of the electrostatic latent image carrier between the completion of the developing step and the start of the charging step, A polishing step of performing a carrier transfer step of transferring the magnetic carrier and a polishing step of polishing the surface of the electrostatic latent image carrier while removing the magnetic carrier by the cleaning unit in this order.
It is characterized by the following.
[0008]
In the first image forming method, the magnetic carrier in the two-component developer is transferred to the electrostatic latent image carrier between the end of the developing step and the start of the charging step in a new image forming processing step. The magnetic carrier is forcibly transferred to the surface, and the transferred magnetic carrier is brought into contact with the surface of the electrostatic latent image carrier, such as a cleaning blade, a fur brush, or the like. Removed (polishing process step). The magnetic carrier transferred to the surface of the electrostatic latent image carrier exerts a polishing action on the surface of the electrostatic latent image carrier when removed by the cleaning means. According to the above, without using toner externally added abrasive fine particles, or without using a special device for polishing the surface of the electrostatic latent image carrier, by simply passing through the above polishing process step, The surface of the electrostatic latent image carrier can be kept clean. Further, according to the first image forming method, the effect of preventing filming can be reliably and efficiently achieved.
[0009]
In the first image forming method according to the present invention, the charge polarity of the toner of the two-component developer used and the effective potential difference between the polishing step and the image forming processing are determined by the magnetic property on the surface of the electrostatic latent image carrier. The setting is made from the viewpoint of efficiently performing the forcible transfer of carriers.
Specifically, in the first image forming method,
The charging polarity of the toner is the same polarity as the surface potential formed on the surface of the electrostatic latent image carrier and the developing bias voltage applied to the surface of the developer carrier in the charging step and the second charging step, and ,
An effective potential difference ΔVep (V) obtained by subtracting a developing bias voltage applied to the surface of the developer carrier in the carrier transfer step from the surface potential formed on the surface of the electrostatic latent image carrier in the second charging step; An effective potential difference ΔVei (V) obtained by subtracting a developing bias voltage applied to the surface of the developer carrier in the developing step from the surface potential formed on the surface of the electrostatic latent image carrier in the charging step is represented by a formula: (1) and (2):
| ΔVep |> | ΔVei | (1)
20 ≦ | ΔVep | − | ΔVei | ≦ 200 (2)
Is preferably set in a range that satisfies the following condition.
[0010]
That is, the charging polarity of the toner in the two-component developer is set to the same polarity as the surface potential formed on the surface of the electrostatic latent image carrier and the developing bias voltage, and the effective potential difference ΔVep in the polishing process and the image forming process The difference ΔVep−ΔVei from the effective potential difference ΔVei is calculated by the following equation when the toner charging polarity is positive:
20 ≦ (ΔVep−ΔVei) ≦ 200
And when the charge polarity of the toner is negative, the following formula:
−200 ≦ (ΔVep−ΔVei) ≦ −20
It is preferable to set so that
[0011]
In the electrophotographic image forming process, in a method of forming a negative latent image and performing reversal development, the surface of the electrostatic latent image carrier is uniformly charged to give a surface potential (initial potential), By exposing the surface to attenuate the portion corresponding to the image portion of the document, a potential difference ΔV having a polarity opposite to the surface potential is generated on the surface. At this time, on the surface of the electrostatic latent image carrier, a difference in surface potential occurs between an exposed portion and a non-exposed portion, so that an electrostatic latent image is formed. Here, the potential difference ΔV is a negative potential difference when the charging potential or the like is positive, and is a positive potential difference when the charging potential or the like is negative. In any case, the potential difference is opposite to the charging polarity of the toner. Polarity. Therefore, the toner adheres to the portion where the potential difference ΔV is generated by the exposure, and the visualization of the electrostatic latent image (formation of the toner image) is realized.
[0012]
On the other hand, the magnetic carrier is charged with a polarity opposite to that of the toner (that is, charged with a polarity opposite to the developing bias voltage and the surface potential of the electrostatic latent image carrier). It is attached to the surface of the carrier by magnetic force.
However, in the first image forming method, the absolute value | ΔVep | of the effective potential difference in the polishing process is set to be larger in a predetermined range than the absolute value | ΔVei | of the effective potential difference in the image forming process. . Therefore, in the polishing process, the magnetic carrier shakes off the potential difference generated from the surface of the developer carrier to the surface of the unexposed electrostatic latent image carrier by the magnetic force of the developer carrier, thereby causing It can be large enough to migrate to the surface. The potential difference generated from the surface of the developer carrier to the surface of the unexposed electrostatic latent image carrier is a positive potential difference when the surface potential of the electrostatic latent image carrier or the developing bias voltage is positive, When the surface potential or the like is negative, the potential difference is a negative potential difference, and in any case, the polarity is opposite to the charging polarity of the magnetic carrier.
[0013]
Specifically, the effective potential difference ΔVep in the polishing process is set to be larger than the effective potential difference ΔVei in the image forming process by 20 to 200 V when the charging potential and the toner charging polarity are positive. When the value is negative, the magnetic carrier is reduced by 20 to 200 V (that is, set so as to satisfy the above expressions (1) and (2)), so that the magnetic carrier is forcibly removed by electrostatic attraction in the polishing process. It can be transferred to the surface of the electrostatic latent image carrier.
[0014]
When the first image forming method according to the present invention is performed by setting the charging polarity of the toner, the effective potential difference ΔVep in the polishing process, and the effective potential difference ΔVei in the image forming process as described above, the difference between ΔVep and ΔVei The magnitude of the difference ΔVep−ΔVei may be set within the above range in consideration of the amount of the magnetic carrier migrating to the surface of the electrostatic latent image carrier (the amount of the magnetic carrier migrating).
When the absolute value | ΔVep−ΔVei | of the difference between ΔVep and ΔVei is less than 20 V, the amount of the magnetic carrier migrating to the surface of the electrostatic latent image carrier decreases, and the polishing effect becomes poor. You will not be able to play enough. On the other hand, when | ΔVep−ΔVei | exceeds 200 V, the amount of magnetic carriers migrating to the surface of the electrostatic latent image carrier increases, the polishing effect becomes excessive, and the surface of the electrostatic latent image carrier is damaged. Or image quality is degraded.
[0015]
| ΔVep−ΔVei | is set according to the amount of transfer of the magnetic carrier as described above, and therefore varies depending on the physical properties of the magnetic carrier and the like. Therefore, the more preferable range of | ΔVep−ΔVei | is not limited alone, but generally, it is particularly preferably 50 to 150 V in the above range.
[0016]
FIG. 1 shows an example of an image forming apparatus for executing the first image forming method. In such an image forming apparatus, first, a charging voltage is uniformly applied from the charger 11 to the surface of the electrostatic latent image carrier (photoconductor drum) 10, and the surface potential is applied to the surface of the electrostatic latent image carrier. (Initial potential) is formed. In the image forming apparatus shown in FIG. 1, a positive surface potential is formed on the surface of the electrostatic latent image carrier 10 by setting the applied voltage to be positive. After charging the surface of the electrostatic latent image carrier, the exposure device 12 exposes the surface of the electrostatic latent image carrier to form a predetermined electrostatic latent image on the surface. The toner 14 charged to the same polarity as the electrostatic latent image carrier moves from the surface of the developer carrier 13 to a portion of the surface of the electrostatic latent image carrier where the positive charge is attenuated by the exposure. Then, the electrostatic latent image is visualized as a toner image. This toner image is transferred onto a transfer target such as paper by a transfer unit such as the transfer charger 15 and is fixed (fixed) on the transfer target by a fixing unit such as a heat roller 17. Thus, a desired image can be formed on the transfer object. On the other hand, the surface of the electrostatic latent image carrier after the transfer process is neutralized by light irradiation from the exposure device 18 or the like, and the toner particles remaining on the surface are removed by cleaning means such as a blade cleaner 19 and a fur brush cleaner. Removed by
[0017]
FIG. 2 shows the relationship between the transition of the surface potential of the electrostatic latent image carrier and the developing bias voltage applied to the surface of the developer carrier in the series of image forming process and polishing process. The relationship between the potential difference and the transfer of the magnetic carrier will be described.
As shown in FIG. 2, when a charging voltage is applied to the surface of the electrostatic latent image carrier (photosensitive drum) 10 (charging step (i)), a predetermined surface potential is generated on the surface (FIG. 2). Is +800 V of (a). In the subsequent exposure step (ii), the exposed portion of the surface of the electrostatic latent image carrier 10 undergoes a surface potential attenuation (in the case of FIG. The potential of the surface is attenuated to +200 V of (b) by exposure.) At this time, a developing bias voltage is applied to the surface of the developer carrier 13 (+600 V in FIG. 2C), and the effective potential difference ΔVei becomes +200 V. Note that a negative potential difference ΔV (−400 V in FIG. 2) is generated from the surface of the developer carrier 13 to the surface of the exposed portion of the electrostatic latent image carrier 10. Due to the negative potential difference ΔV, the toner moves from the surface of the developer carrier 13 to the exposed portion of the electrostatic latent image carrier 10, and the electrostatic latent image is visualized as a toner image. Note that (iii) in FIG. 2 indicates that the surface potential of the electrostatic latent image carrier has disappeared by the charge removal step after the transfer processing.
[0018]
On the other hand, in the polishing step (iv), the same charging voltage (a) as in the charging step (i) is applied to the surface of the electrostatic latent image carrier 10, but the surface is not exposed. The developing bias voltage (d) applied to the surface of the developer carrier is set lower than in the developing step (+200 V in (d) in FIG. 2). Therefore, the effective potential difference ΔVep in the polishing step is larger than the effective potential difference ΔVei generated in the exposure step. In the case shown in FIG. 2, the absolute value | ΔVep | of the effective potential difference during the polishing process is 200 V larger than the absolute value | ΔVei | of the effective potential difference during the development process.
[0019]
Here, the toner is charged to the same positive polarity as the electrostatic latent image carrier, and the potential difference from the surface of the developer carrier to the surface of the electrostatic latent image carrier is positive. It does not migrate to the surface of the carrier. On the other hand, the magnetic carrier charged to the opposite negative polarity to the electrostatic latent image carrier and the developer carrier has an effective potential difference that is set to be larger than that in the exposure and development steps. The transfer of the developer carrier to the surface of the electrostatic latent image carrier is released by removing the constraint of the developer carrier by the magnetic force. The difference between the absolute value of the effective potential difference ΔVep and the absolute value of ΔVei is set such that the transfer of the magnetic carrier is realized and the transfer amount is in an appropriate range.
[0020]
In the first image forming method, the transfer of the magnetic carrier to the surface of the electrostatic latent image carrier is performed by completing a new series of image forming processing steps (charging, exposure, development, transfer, charge removal, It may be performed before the start of the charging step (first charging step) in each step of the cleaning. That is, the above-described polishing process may be performed by sewing a gap at the time of image formation or at the time of so-called non-image formation.
Therefore, according to the first image forming method, the magnetic carrier is not mixed in the toner image obtained by visualizing the electrostatic latent image, and there is a possibility that an image defect such as a so-called white spot is generated in the formed image. There is no.
[0021]
In the first image forming method according to the present invention, the frequency of the polishing step, the amount of the magnetic carrier transferred to the surface of the electrostatic latent image carrier in the step, and the application of the charging voltage in the second charging step The time may be set in consideration of the degree of the polishing effect on the surface of the electrostatic latent image carrier.
In particular,
(A) performing the polishing process every time the image forming process is performed for 1 to 100 cycles;
(B) setting the total amount of the magnetic carrier migrating to the surface of the electrostatic latent image carrier in the carrier migrating process to be 0.02 to 0.2 g when the image forming process is repeated 1000 cycles; and
(C) in the second charging step, the time for applying a charging voltage to the surface of the electrostatic latent image carrier is set to 0.1 to 0.3 seconds;
It is preferable that at least one of them is satisfied.
[0022]
(A) Frequency of polishing process
In the first image forming method according to the present invention, the frequency of the polishing process is one cycle of the image forming process if the purpose is to simply maintain the clean state of the surface of the electrostatic latent image carrier. It is most preferable to perform the polishing process every time. On the other hand, it is necessary to consider a decrease in the productivity of the image forming process and an increase in the amount of wear of the electrostatic latent image carrier (the accompanying reduction in the life of the electrostatic latent image carrier).
[0023]
In the first image forming method according to the present invention, as described above, it is preferable that the polishing process is performed until the number of elapsed times of the image forming process exceeds 100 cycles. If the frequency of the polishing process is less than the above frequency (the number of cycles is large), the effect of polishing the surface of the electrostatic latent image carrier becomes poor, and the effect of the present invention may not be sufficiently exhibited. is there.
The frequency of performing the polishing treatment step is a degree of the polishing effect, specifically, is set according to the transfer amount of the magnetic carrier, the physical properties of the magnetic carrier, and the like. It is preferable to set so that the image forming process is executed every 1 to 20 cycles.
[0024]
(B) Transfer amount of magnetic carrier
In the first image forming method according to the present invention, the total amount of the magnetic carrier transferred to the surface of the electrostatic latent image carrier (total amount of transfer of the magnetic carrier) is determined by the degree to which the surface of the electrostatic latent image carrier is polished and the formation. The value is set in the above range while considering the influence on the quality of the image.
If the total transfer amount of the magnetic carrier per 1000 cycles of the image forming process is less than 0.02 g, the effect of polishing the surface of the electrostatic latent image carrier becomes poor, and the effect of the present invention may not be sufficiently exhibited. There is. Conversely, if the total transfer amount of the magnetic carrier per 1000 cycles of the image forming process exceeds 0.2 g, the polishing effect becomes too large, and the surface of the electrostatic latent image carrier may be damaged. Further, in this case, the mixing ratio of the magnetic carrier in the toner image on the electrostatic latent image carrier becomes too high, so that a defect such as a so-called white spot may occur in a formed image, and the image quality may be degraded.
[0025]
As described above, the total transfer amount of the magnetic carrier is set according to the degree of the polishing effect on the surface of the electrostatic latent image carrier, the effect on the quality of the formed image, and the like, and also depends on the physical properties of the magnetic carrier. It can fluctuate. Therefore, the more preferable range of the total transfer amount of the magnetic carrier is not particularly limited, but generally, it is particularly preferably 0.05 to 0.1 g in the above range.
[0026]
(C) Charging voltage application time
In the first image forming method according to the present invention, the time during which the charging voltage is applied to the surface of the electrostatic latent image carrier in the second charging step (during the polishing process) is different from the time required for applying the charging voltage to the surface of the electrostatic latent image carrier. The amount is set in the above range according to the amount of the magnetic carrier to be transferred (the transfer amount of the magnetic carrier), while taking into account the degree of polishing the surface of the electrostatic latent image carrier and the effect on the quality of the formed image. .
[0027]
When the application time of the charging voltage in the second charging step is less than 0.1 second, the amount of the magnetic carrier migrating to the surface of the electrostatic latent image carrier decreases, and the polishing effect on the surface may be reduced. . Conversely, if the application time of the charging voltage in the second charging step exceeds 0.3 seconds, the amount of the magnetic carrier migrating to the surface of the electrostatic latent image carrier increases, and the polishing effect on the surface becomes excessive. Could be.
The application time of the charging voltage in the second charging step also depends on the physical properties of the magnetic carrier, the ease of transfer to the surface of the electrostatic latent image carrier, the rotation speed of the electrostatic latent image carrier and the developer carrier, and the like. It can fluctuate. Accordingly, the more preferable range of the charging voltage application time is not particularly limited, but generally, it is particularly preferably 0.15 to 0.25 seconds in the above range.
[0028]
In the first image forming method according to the present invention, the range of the particle diameter of the magnetic carrier in the two-component developer used is determined from the viewpoint of setting the degree of polishing of the surface of the electrostatic latent image carrier to an appropriate range. It is preferable to set.
Specifically, in the two-component developer used in the first image forming method, the magnetic carrier in the two-component developer contains 1 to 30% by weight of the magnetic carrier passing through a mesh of 30 μm in the total magnetic carrier. It is preferable that they are contained in proportions.
[0029]
The particle size of the magnetic carrier having a small particle size in the magnetic carrier is set in consideration of the polishing effect on the surface of the electrostatic latent image carrier. If the particle size of the magnetic carrier is large, there is a possibility that the magnetic carrier may cause a problem that the surface of the electrostatic latent image carrier is damaged. The particle size of the small-diameter magnetic carrier preferably passes through a mesh having a mesh size of 20 μm, particularly in the above range.
In the two-component developer, the content ratio of the small-diameter magnetic carrier is set so as to be 1 to 30% by weight in all the magnetic carriers in consideration of the transfer amount of the magnetic carrier. When the content ratio of the small-diameter magnetic carrier in all the magnetic carriers is less than the above range, the amount of the magnetic carrier migrating to the surface of the electrostatic latent image carrier decreases, and the amount required by the second image forming method is reduced. There is a possibility that the amount of transfer will not be reached. On the other hand, when the content ratio of the small-diameter magnetic carrier exceeds the above range, the amount of the magnetic carrier migrating to the surface of the electrostatic latent image carrier becomes too large, and the migrating required for the second image forming method is performed. May exceed the amount. The content ratio of the small-diameter magnetic carrier in all the magnetic carriers is particularly preferably 3 to 20% by weight in the above range.
[0030]
(Image forming apparatus used in first image forming method)
The image forming apparatus according to the present invention is used for the first image forming method. In particular, in the first image forming method, the charging polarity of the toner in the two-component developer used is the same as the surface potential of the electrostatic latent image carrier and the developing bias voltage, and during the polishing step. Is particularly preferable when the effective potential difference ΔVep of the above and the effective potential difference ΔVei at the time of image forming processing satisfy the above-mentioned expressions (1) and (2).
[0031]
The image forming apparatus includes:
An electrostatic latent image carrier,
Charging means for applying a charging voltage to the surface of the electrostatic latent image carrier,
Exposure means for forming an electrostatic latent image on the surface of the electrostatic latent image carrier,
A developer carrying member carrying a toner and a magnetic carrier on the surface,
Developing bias applying means for applying a developing bias voltage having the same polarity as the charging polarity of the toner to the surface of the developer carrier,
Transfer means for transferring the toner image formed on the surface of the electrostatic latent image carrier to a transfer target,
Cleaning means for removing, from the surface of the electrostatic latent image carrier, toner remaining on the surface of the electrostatic latent image carrier after transfer processing of the toner image and magnetic carriers transferred to the surface of the electrostatic latent image carrier;
An effective potential difference ΔVep (V) obtained by subtracting a developing bias voltage in the carrier transfer step from a surface potential formed on the surface of the electrostatic latent image carrier in the second charging step; The effective potential difference ΔVei (V) obtained by subtracting the developing bias voltage in the developing step from the surface potential formed on the surface of the body is expressed by the following equations (1) and (2):
| ΔVep |> | ΔVei | (1)
20 ≦ | ΔVep | − | ΔVei | ≦ 200 (2)
Means for controlling the applied voltage to be set in a range satisfying
It is characterized by having.
[0032]
According to the image forming apparatus of the present invention, the surface of the electrostatic latent image carrier is uniformly charged by the charging unit after the developing process is completed and before the charging process in the new image forming process is started. (Second charging step), and by adjusting the intensity of the developing bias voltage applied to the surface of the developer carrier by the control means, the magnetic carrier is moved from the developer carrier to the electrostatic latent image carrier. Can be forcibly transferred (electrostatic suction) to the surface (carrier transfer step).
In the above-described image forming apparatus, in order to realize forcible transfer of the carrier, as a two-component developer, the charge polarity of the toner is changed to the surface potential formed on the surface of the electrostatic latent image carrier and the surface of the developer carrier. And the absolute value of the effective potential difference obtained by subtracting the developing bias voltage during the polishing process from the surface potential of the electrostatic latent image carrier during the polishing process is used. | ΔVep | is 20 to 200 V larger than the absolute value | ΔVei | of the effective potential difference obtained by subtracting the developing bias voltage in the series of steps from the surface potential of the electrostatic latent image carrier in the series of steps (image forming processing). It is adjusted by the above-mentioned control means.
[0033]
Therefore, according to the image forming apparatus, it is possible to forcibly transfer the magnetic carrier in the two-component developer to the surface of the electrostatic latent image carrier at the time of non-image formation. The surface can be polished by removing it from the surface of the electrostatic latent image carrier by a cleaning means such as a cleaning blade or a fur brush. That is, according to the above-described image forming apparatus, a special device for polishing the surface of the electrostatic latent image carrier is not provided, and polishing is performed during non-image formation without using a toner to which abrasive fine particles are externally added. By performing the steps, the polishing process on the surface of the electrostatic latent image carrier can be performed.
[0034]
(Second image forming method)
A second image forming method according to the present invention includes:
A charging step of uniformly charging the surface of the electrostatic latent image carrier, an exposure step of exposing the surface of the electrostatic latent image carrier to form an electrostatic latent image, A developing step of visualizing the electrostatic latent image with the applied toner, a transfer step of transferring the toner image formed on the electrostatic latent image carrier by the visualization onto a transfer target, A cleaning step of bringing a cleaning unit into contact with the surface of the image carrier, and
As the toner, a toner whose charge polarity is the same polarity as the surface potential formed on the surface of the electrostatic latent image carrier and the developing bias voltage applied to the surface of the developer carrier by the charging step,
As the magnetic carrier, a magnetic carrier having a saturation magnetization of 45 to 55 emu / g and a magnetic carrier passing through a mesh having an opening of 30 μm in a proportion of 3 to 20% by weight is used,
The spontaneous transfer amount of the magnetic carrier from the surface of the developer carrier to the surface of the electrostatic latent image carrier in the developing step is determined by a series of image forming processing steps including the charging, exposure, development, transfer and cleaning of 1000 cycles. It is set to be 0.02-0.2 g when repeated, and
The magnetic carrier transferred to the surface of the electrostatic latent image carrier is removed from the surface of the electrostatic latent image carrier by the cleaning means in the cleaning step.
It is characterized by the following.
[0035]
In the second image forming method, in the developing step, the magnetic carrier having low saturation magnetization contained in the two-component developer spontaneously moves from the surface of the developer carrier to the surface of the electrostatic latent image carrier. . The magnetic carrier that has migrated to the surface of the electrostatic latent image carrier, together with the toner remaining on the surface of the electrostatic latent image carrier after the transfer step, is cleaned by a cleaning means such as a cleaning blade or a fur brush. However, during the removal process, the magnetic carrier polishes the surface of the electrostatic latent image carrier. Therefore, according to the second image forming method, there is no need to use a toner to which abrasive fine particles are externally added or a special device for polishing the surface of the electrostatic latent image carrier, or the second image forming method according to the present invention. The charging, exposure, development, transfer, and cleaning steps can be performed without performing special control on the surface potential of the electrostatic latent image carrier and the developing bias voltage of the developer carrier as in the image forming method of (1). The surface of the electrostatic latent image carrier can be polished only by executing a series of image forming processes including the above, and a clean state of the surface can be maintained. In addition, the effect of preventing filming can be surely and efficiently achieved.
[0036]
In the above-described second image forming method, the toner in the two-component developer has a charging polarity of a surface potential formed on the surface of the electrostatic latent image carrier and a development applied to the surface of the developer carrier. One having the same polarity as the bias voltage is used.
In the above-described second image forming method, the range of the degree of magnetization and the range of the particle size of the magnetic carrier means that the spontaneous transfer of the magnetic carrier to the surface of the electrostatic latent image carrier is efficiently performed and the range of the transfer amount In addition, it is preferable to set the degree of polishing effect on the surface of the electrostatic latent image carrier from an appropriate viewpoint.
Specifically, the magnetic carrier in the two-minute developer used in the second image forming method is a magnetic carrier having a saturation magnetization of 45 to 55 emu / g and passing through a mesh of 30 μm in all the magnetic carriers. (Low saturation magnetization and small particle size magnetic carrier) at a ratio of 3 to 20% by weight.
[0037]
The magnetic carrier is charged with a polarity opposite to that of the toner, that is, charged with a polarity opposite to the developing bias voltage or the surface potential of the electrostatic latent image carrier. The magnetic carrier is usually attached to the surface of the developer carrier mainly by magnetic force. However, the magnetic carrier having a low saturation magnetization is easily transferred from the surface of the developer carrier to the surface of the electrostatic latent image carrier in the developing step by electrostatic attraction. This is remarkable especially among magnetic carriers having a low saturation magnetization, particularly those having a small particle diameter.
[0038]
The value of the saturation magnetization for the low saturation magnetization and small particle size magnetic carrier is determined by considering the ease of electrostatic attraction to the surface of the electrostatic latent image carrier, The transfer amount (total amount) of the magnetic carrier when the cycle is repeated is appropriately set in the above-described range of 45 to 55 emu / g such that the transfer amount (total amount) becomes 0.02 to 0.2 g.
If the saturation magnetization of the low saturation magnetization and small particle size magnetic carrier is below the above range, the transfer amount of the magnetic carrier to the surface of the electrostatic latent image carrier increases, the polishing effect becomes excessive, and the surface is scratched. A problem such as sticking occurs. On the other hand, when the saturation magnetization exceeds the above range, the transfer amount of the magnetic carrier becomes small and the polishing effect becomes poor, so that the effect of the present invention cannot be sufficiently exhibited. The saturation magnetization of the low saturation magnetization and small particle size magnetic carrier is more preferably 48 to 53 emu / g in the above range.
[0039]
The particle size of the low saturation magnetization / small particle size magnetic carrier is limited to those passing through a mesh having openings of 30 μm in consideration of the polishing effect on the surface of the electrostatic latent image carrier. If the particle size of the low saturation magnetization, small particle size magnetic carrier does not satisfy the above conditions (the particle size is large), the magnetic carrier may damage the surface of the electrostatic latent image carrier. May occur. It is preferable that the particle diameter of the low saturation magnetization and small particle diameter magnetic carrier passes through a mesh having a mesh size of 20 μm, particularly in the above range.
[0040]
The content ratio of the low saturation magnetization and small particle size magnetic carrier is set so as to be 3 to 20% by weight in all the magnetic carriers in consideration of the transfer amount of the magnetic carrier. When the content ratio of the low saturation magnetization and small particle size magnetic carrier in all the magnetic carriers is below the above range, the amount of the magnetic carrier spontaneously migrating to the surface of the electrostatic latent image carrier becomes too small, and There is a possibility that the transfer amount required in the image forming method 2 may not be reached. Conversely, if the content ratio of the low saturation magnetization, small particle size magnetic carrier exceeds the above range, the amount of the magnetic carrier which spontaneously migrates to the surface of the electrostatic latent image carrier becomes too large, and the second image There is a possibility that the transfer amount required for the forming method may be exceeded. Further, when the content ratio exceeds the above range, a sufficient charge amount may not be provided to the toner of the two-component developer. The content ratio of the low saturation magnetization / small particle size magnetic carrier in all the magnetic carriers is particularly preferably 5 to 10% by weight in the above range.
[0041]
In the second image forming method according to the present invention, the amount of the magnetic carrier to be transferred to the surface of the electrostatic latent image carrier (the transfer amount of the magnetic carrier) depends on the degree to which the surface of the electrostatic latent image carrier is polished, The setting is made in consideration of the influence on the quality of the formed image. Specifically, as described above, when the above series of steps is repeated 1000 cycles (when a series of image forming processes is performed 1000 times), the transfer amount (total amount) of the magnetic carrier is 0.02 to 0. It is set to be 2 g.
[0042]
When the transfer amount (total amount) of the magnetic carrier per 1000 cycles of the series of image forming processing steps is less than 0.02 g, the effect of polishing the surface of the electrostatic latent image carrier becomes poor, and the effect of the present invention is sufficiently exhibited. You can't do that. Conversely, if the transfer amount (total amount) of the magnetic carrier per 1000 cycles of the series of image forming processing steps exceeds 0.2 g, the polishing effect becomes too large, and the surface of the electrostatic latent image carrier is damaged. As a result, problems such as generation of black spots occur. Alternatively, the mixing ratio of the magnetic carrier in the toner image obtained by visualizing the electrostatic latent image becomes high, so that a defect such as a so-called white spot occurs in the formed image, and the image quality deteriorates.
[0043]
As described above, the transfer amount of the magnetic carrier is set according to the degree of the polishing effect on the surface of the electrostatic latent image carrier, the effect on the quality of the formed image, and the like. It varies depending on Therefore, the more preferable range of the transfer amount of the magnetic carrier is not limited alone, but in general, it is particularly preferably 0.05 to 0.1 g in the above range.
The problem when the transfer amount (total amount) of the magnetic carrier per 1000 cycles of the image forming process deviates from the above range and the more preferable range of the transfer amount are the same as in the case of the first image forming method.
[0044]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the image forming method of the present invention, the two-component developer used for the method, and the image forming apparatus will be described in detail.
[0045]
[First image forming method and image forming apparatus used therein]
In the first image forming method according to the present invention, the transfer amount of the magnetic carrier to the surface of the electrostatic latent image carrier is set according to the effect on the polishing effect of the surface as described above. It is.
Factors affecting the polishing effect on the surface of the electrostatic latent image carrier include, for example, the surface hardness of the magnetic carrier, the shape of the carrier particles, and the like. When the magnetic carrier is hard or has many irregularities on the surface, the polishing effect is generally increased. Therefore, it is preferable to set the transfer amount of the carrier to be small. Conversely, when the magnetic carrier is soft or has a smooth surface, the polishing effect is generally reduced, so that it is preferable to set the transfer amount of the carrier to be large.
On the other hand, factors affecting the quality of the formed image (image quality) include, for example, the particle size of the magnetic carrier. When the magnetic carrier has a large particle size, the influence on the toner image obtained in the developing step becomes too large. Therefore, it is preferable to set the transfer amount of the carrier to be small.
[0046]
Regarding the two-component developer used in the first image forming method, the charging polarity of the toner is determined by the surface potential formed on the surface of the electrostatic latent image carrier in the charging step and the second charging step, and There is no particular limitation, other than having the same polarity as the developing bias voltage, and preferably containing a small particle size magnetic carrier at a predetermined ratio.
Accordingly, various conventionally known toners can be used. The toner to be used may contain various compounding agents such as a charge controlling agent and a wax in addition to the binder resin and the colorant. Fine particles such as a fluidizing agent may be externally added (externally added) to the outer surface of the toner.
[0047]
As the magnetic carrier, various conventionally known magnetic carriers are used, except that the content ratio of a magnetic carrier having a predetermined saturation magnetization and a particle size (low saturation magnetization / small particle size magnetic carrier) is set in a predetermined range. can do. That is, various known materials may be used for the magnetic particles constituting the magnetic carrier and the coat layer covering the surface thereof.
[0048]
The cleaning means used for removing the toner remaining on the surface of the electrostatic latent image carrier in the cleaning step and removing the magnetic carrier transferred to the surface of the electrostatic latent image carrier in the polishing step is as described above. As described above, various conventionally known cleaning means such as a cleaning blade and a fur brush can be employed.
[0049]
As an image forming apparatus for performing the first image forming method according to the present invention, means for executing the above-described series of image forming processing steps, that is, the above-described electrostatic latent image carrier, charging means, and exposure means Any means may be used as long as the apparatus includes a developer carrier, a developing bias applying unit, a transferring unit, a cleaning unit, and an applied voltage controlling unit.
Of these means, the electrostatic latent image carrier, charging means, exposure means, developer carrier, developing bias applying means, transfer means, and cleaning means are not particularly limited, and various conventionally known images can be used. Means similar to those used in the forming apparatus can be employed.
[0050]
[Second image forming method]
In the second image forming method according to the present invention, the transfer amount of the magnetic carrier to the surface of the electrostatic latent image carrier depends on the polishing effect on the surface and the influence on the quality of the formed image as described above. Is set. Factors affecting the polishing effect on the surface of the electrostatic latent image carrier include the same as those exemplified in the first image forming method.
[0051]
Among the two-component developers used in the second image forming method, the content ratio of the low saturation magnetization and small particle size magnetic carrier is determined as described above. It is set in consideration of the shift amount. Specifically, it depends on the toner concentration (T / D) in the two-component developer and the degree of the polishing effect of the magnetic carrier on the electrostatic latent image carrier (surface hardness of the magnetic carrier, shape of particles, etc.). Thus, it may be set appropriately from the above range.
[0052]
The two-component developer used in the second image forming method has the same charge polarity of the toner as the surface potential formed on the surface of the electrostatic latent image carrier and the same polarity as the developing bias voltage. The magnetic carrier is not particularly limited except that the magnetic carrier contains the above-mentioned low saturation magnetization and small particle size magnetic carrier at a predetermined ratio.
Therefore, various conventionally known toners can be used as the toner used in the first image forming method.
Further, as the magnetic carrier, various conventionally known magnetic carriers can be used as in the case of the magnetic carrier used in the first image forming method.
As a cleaning means for removing the toner remaining on the surface of the electrostatic latent image carrier and the magnetic carrier transferred to the surface, various types of conventionally known cleaning blades and fur brushes are used as described above. Cleaning means can be employed.
[0053]
The image forming apparatus for performing the second image forming method according to the present invention is not particularly limited, except that it can execute the above-described series of image forming processing steps. Image forming apparatuses using various electrophotographic methods can be adopted.
[0054]
【Example】
Next, the present invention will be described with reference to Examples and Comparative Examples.
[0055]
[Example of First Image Forming Method]
Using the first image forming method according to the present invention, an image forming test using an actual machine was performed. In the test, a two-component developer containing a toner and a magnetic carrier was used.
Among these developers, a positively charged toner (average particle size 9 μm) using a styrene-acryl resin as a binder resin was used as the toner.
As the magnetic carrier, a coated carrier (weight average particle size: 60 μm) in which a surface of ferrite particles was coated with a silicone resin was used. The magnetic carriers include those passing through a mesh having an opening of 30 μm and those not passing through the mesh, and the saturation magnetization of each of them was 60 emu / g. Further, the content ratio of those passing through the mesh was 10% by weight in all the magnetic carriers.
The mixing ratio between the toner and the magnetic carrier was adjusted to be 5:95 (weight ratio).
[0056]
(Example 1)
In the image forming test, an electrophotographic copying machine manufactured by Kyocera Mita Co., Ltd. [model modified from "KM-5530") was used as an image forming apparatus. This electrophotographic copying machine forms an image by a positive charge reversal development system.
[0057]
In the image forming test, the peripheral speed of the surface of the electrostatic latent image carrier (photoconductor) was 300 mm / sec, and the ratio of the peripheral speed of the developer carrier (developing sleeve) to the peripheral speed of the photoconductor (S / D) is 2.7, the cutting edge height of the developing sleeve is 0.5 mm, the distance between the photoconductor and the developing sleeve is 0.5 mm, the main magnetic pole force of the developing sleeve is 1000 Gs (Gauss), The position of the main pole of the developing sleeve is + 2.0 ° (upstream in the rotation direction), and the bias voltage of the developing sleeve (developing bias voltage) is +600 V (during the image forming process) and +580 V (during the polishing process). The light potential of the body was set to +150 V in both the image forming process and the polishing process, and the dark potential was set to +800 V in both the image forming process and the polishing process. The environmental conditions during the image forming test were room temperature of 20 ° C. and humidity of 60% RH.
The surface potential of the photoreceptor is a value obtained by measuring a voltage generated by a charge carried on the surface of the photoreceptor, which is measured at a developing nip portion which is a closest portion between the photoreceptor and the developing sleeve. The surface potential was measured using a surface potentiometer “model 344” manufactured by TREK, and the distance between the measurement probe and the surface of the photoconductor was about 3 mm.
[0058]
In Example 1, the effective potential difference ΔVep during the polishing step was +220 V, and the effective potential difference ΔVei during the image forming process was +200 V, satisfying the relationship of | ΔVep |> | ΔVei |. | ΔVep | − | ΔVei | was 20 V.
The polishing step was performed every time a series of image forming processing steps including charging, exposure, development, transfer and cleaning steps were repeated for one cycle.
Using the above-described image forming apparatus and the two-component developer, the image forming process (copying process) of an A4 size black character original (black ratio 6%) was repeated 300,000 cycles under the above conditions.
[0059]
(Example 2 and Comparative Examples 1 and 2)
The developing bias voltage during the polishing step is +400 V (Example 2), +600 V (Comparative Example 1) or +380 V (Comparative Example 2), and the dark potential is +800 V both during the image forming process and during the polishing process. Thus, the image forming process (copying process) was performed in the same manner as in Example 1, except that the effective potential difference ΔVep and the value of | ΔVep | − | ΔVei | during the polishing step were set to the values shown in Table 1, respectively. Was repeated 300,000 cycles. The frequency of execution of the polishing step was the same as in Example 1.
[0060]
(Evaluation of polishing process)
In the above embodiment and the comparative example, as in the case of the embodiment according to the first image forming method, every time a series of image forming processes is repeated 1000 cycles, the amount of magnetic carrier mixed in The amount of the magnetic carrier consumed from the component developer was measured. Further, by visually observing the surface state of the electrostatic latent image carrier and the presence or absence of filming, the polishing effect of the electrostatic latent image carrier (photoconductor) with the magnetic carrier was evaluated.
The transfer amount (g) of the magnetic carrier to the surface of the electrostatic latent image carrier was calculated based on the mixed amount of the magnetic carrier in the collected toner.
[0061]
Table 1 shows the above results.
[0062]
[Table 1]

[0063]
In Table 1, "Transfer amount of magnetic carrier" indicates the transfer amount (g) when the above series of image forming processes is repeated for 1000 cycles. "-" In the column of "Evaluation result" indicates that scratches or filming occurred on the surface of the electrostatic latent image carrier (photoconductor) even after the above series of image forming apparatus was repeated for 300,000 cycles. Indicates that was not confirmed. In the same column, "... scratches occur on every 10,000 sheets" or "... filming occurs on every 10,000 sheets" means that the above-described series of image forming apparatuses is repeated ... This indicates that the occurrence of scratches or filming was confirmed on the surface.
[0064]
As is evident from Table 2, in the embodiment in which the image was formed by the second image forming method of the present invention, even after repeating the above series of image forming processes for a very large number of 300,000 cycles. In addition, there was no problem that scratches and filming occurred on the surface of the electrostatic latent image carrier.
On the other hand, in the comparative example, when | ΔVep | − | ΔVei | is too small, a problem occurs that filming occurs on the surface of the electrostatic latent image carrier, and conversely, | ΔVep | − | When ΔVei | is too large, there is a problem that the surface of the electrostatic latent image carrier is damaged. It is presumed that the cause is that the transfer amount of the magnetic carrier is too small in the former case, and the transfer amount of the magnetic carrier is too large in the latter case.
[0065]
[Example of Second Image Forming Method]
Using the second image forming method according to the present invention, an image forming test using an actual machine was performed. In the test, a two-component developer containing a toner and a magnetic carrier was used.
Among the developers, the used toner and the mixing ratio of the toner and the magnetic carrier are the same as in the “Example by First Image Forming Method”.
As the magnetic carrier, a coated carrier in which the surface of ferrite particles was coated with a silicone resin was used. This magnetic carrier has a weight average particle size of 60 μm, and includes those that have passed through a mesh having an opening of 30 μm and those that have not passed through the mesh. The saturation magnetization was 60 emu / g. The saturation magnetization and the content ratio of those having passed through a mesh having an opening of 30 μm were appropriately adjusted for each Example and Comparative Example.
The saturation magnetization was measured using a magnetic measurement tester “BHU-60” manufactured by RIKEN ELECTRONICS CO., LTD. Under a condition where a magnetic field of 3,000 Oe was applied.
[0066]
(Example 3)
In the image forming test, as in the case of Example 1, an electrophotographic copying machine [a modified version of "KM-5530" described above) was used as an image forming apparatus. Circumferential speed on the surface of the electrostatic latent image carrier (photoconductor), peripheral speed ratio (S / D) between the developer carrier (developing sleeve) and the photoconductor, cutting edge height of the developing sleeve, photoconductor-developing sleeve The distance, the magnetic force of the main pole of the developing sleeve and its position, and the environmental conditions at the time of the test were all the same as those of the "Example by the first image forming method".
The bias voltage (development bias voltage) of the developing sleeve was set at +600 V, the light potential of the photoconductor was set at +150 V, and the dark potential was set at +800 V.
[0067]
In Example 3, among the magnetic carriers of the two-component developer, those having passed through a mesh having a mesh size of 30 μm had a saturation magnetization of 45 emu / g, and the magnetic carrier of all the magnetic carriers having passed through the mesh was used. Was adjusted to 20% by weight, respectively.
Using the above-described image forming apparatus and the two-component developer, the image forming process (copying process) of an A4 size black character original (black ratio 6%) was repeated 300,000 cycles under the above conditions.
[0068]
(Example 4 and Comparative Examples 3 to 6)
Among the magnetic carriers of the two-component developer, those having a saturation magnetization of 55 emu / g (Example 2 and Comparative Example 4), 45 emu / g (Comparative Example 3), and 44 emu / g are assumed to have passed through a mesh having an aperture of 30 μm. (Comparative Example 5) or 56 emu / g (Comparative Example 6) was used, and the content ratio of the magnetic carrier that passed through the mesh in all the magnetic carriers was 3% by weight (Example 2 and Comparative Example 6). ), 21% by weight (Comparative Example 3), 2% by weight (Comparative Example 4) or 20% by weight (Comparative Example 5).
The image forming process (copying process) was repeated 300,000 cycles in the same manner as in Example 3 except that the two-component developer was used.
[0069]
(Evaluation of polishing effect)
In the above Examples and Comparative Examples, each time a series of image forming processes including charging, exposure, development, transfer, and cleaning processes is repeated for 1000 cycles, the amount of magnetic carrier mixed in The amount of the magnetic carrier consumed from the developer was measured. Further, by visually observing the surface state of the electrostatic latent image carrier and the presence or absence of filming, the polishing effect of the electrostatic latent image carrier (photoconductor) with the magnetic carrier was evaluated.
The transfer amount (g) of the magnetic carrier to the surface of the electrostatic latent image carrier was calculated based on the mixed amount of the magnetic carrier in the collected toner.
[0070]
Table 2 shows the above results.
[0071]
[Table 2]

[0072]
In Table 2, the term “low saturation magnetization / small particle size magnetic carrier” refers to a magnetic carrier that has passed through a mesh having an aperture of 30 μm. “Transfer amount of magnetic carrier” indicates the transfer amount (g) when the above series of image forming processes is repeated for 1000 cycles. "-" In the column of "Evaluation result" indicates that scratches or filming occurred on the surface of the electrostatic latent image carrier (photoconductor) even after the above series of image forming apparatus was repeated for 300,000 cycles. Indicates that was not confirmed. In the same column, "... scratches occur on every 10,000 sheets" or "... filming occurs on every 10,000 sheets" means that the above-described series of image forming apparatuses is repeated on every ... This indicates that the occurrence of scratches or the occurrence of filming was confirmed.
[0073]
As is clear from Table 2, the present invention uses a two-component developer containing a predetermined ratio of a low-saturation-magnetization / small-particle-diameter magnetic carrier in which the saturation magnetization and the particle size are set in a predetermined range. In the embodiment in which the image is formed by the second image forming method, even after repeating the series of image forming processes as many as 300,000 cycles, an extremely large number of times, the surface of the electrostatic latent image carrier is still in use. There was no problem that scratches and filming occurred.
[0074]
On the other hand, in the comparative example, when the saturation magnetization of the low-saturation-magnetization / small-particle-size magnetic carrier is too low or the content ratio thereof is too large, a problem occurs that the surface of the electrostatic latent image carrier is damaged. Conversely, when the saturation magnetization of the low saturation magnetization and small particle size magnetic carrier is too high or the content ratio thereof is too low, filming occurs on the surface of the electrostatic latent image carrier. It is presumed that the cause is that the transfer amount of the magnetic carrier is too large in the former case, and the transfer amount of the magnetic carrier is too small in the latter case.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus.
FIG. 2 is an explanatory diagram showing a relationship between a transition of a surface potential of an electrostatic latent image carrier and a developing bias voltage applied to the surface of a developer carrier.

Claims (8)

At least a charging step of uniformly charging the surface of the electrostatic latent image carrier, an exposure step of exposing the surface of the electrostatic latent image carrier to form an electrostatic latent image, and a surface of the developer carrier A developing step of visualizing the electrostatic latent image with the toner carried on the toner, a transfer step of transferring the toner image formed on the electrostatic latent image carrier by the visualization onto a transfer-receiving body, A cleaning step of bringing a cleaning unit into contact with the surface of the electrostatic latent image carrier; and
A second charging step of uniformly charging the surface of the electrostatic latent image carrier between the completion of the developing step and the start of the charging step, A polishing step of performing a carrier transfer step of transferring the magnetic carrier, and a polishing step of polishing the surface of the electrostatic latent image carrier while removing the magnetic carrier by the cleaning unit in this order. Image forming method. The charging polarity of the toner is the same polarity as the surface potential formed on the surface of the electrostatic latent image carrier and the developing bias voltage applied to the surface of the developer carrier in the charging step and the second charging step, And,
An effective potential difference ΔVep (V) obtained by subtracting a developing bias voltage applied to the surface of the developer carrier in the carrier transfer step from the surface potential formed on the surface of the electrostatic latent image carrier in the second charging step; An effective potential difference ΔVei (V) obtained by subtracting a developing bias voltage applied to the surface of the developer carrier in the developing step from the surface potential formed on the surface of the electrostatic latent image carrier in the charging step is represented by a formula: (1) and (2):
| ΔVep |> | ΔVei | (1)
20 ≦ | ΔVep | − | ΔVei | ≦ 200 (2)
2. The image forming method according to claim 1, wherein the range is set to satisfy the following condition. 3. The image forming method according to claim 1, wherein the polishing process is performed every time the image forming process is performed for 1 to 100 cycles. 4. The method according to claim 1, wherein the total amount of the magnetic carrier transferred to the surface of the electrostatic latent image carrier in the carrier transfer step is set to be 0.02 to 0.2 g when the image forming processing step is repeated 1000 cycles. 3. The image forming method according to item 2. 3. The image forming method according to claim 1, wherein in the second charging step, the time for applying a charging voltage to the surface of the electrostatic latent image carrier is 0.1 to 0.3 seconds. The image forming method according to claim 1, wherein the magnetic carrier contains a magnetic carrier passing through a mesh having an opening of 30 μm in a ratio of 1 to 30% by weight in all the magnetic carriers. An image forming apparatus used in the image forming method according to claim 1,
An electrostatic latent image carrier,
Charging means for applying a charging voltage to the surface of the electrostatic latent image carrier,
Exposure means for forming an electrostatic latent image on the surface of the electrostatic latent image carrier,
A developer carrying member carrying a toner and a magnetic carrier on the surface,
Developing bias applying means for applying a developing bias voltage having the same polarity as the charging polarity of the toner to the surface of the developer carrier,
Transfer means for transferring the toner image formed on the surface of the electrostatic latent image carrier to a transfer target,
Cleaning means for removing, from the surface of the electrostatic latent image carrier, toner remaining on the surface of the electrostatic latent image carrier after transfer processing of the toner image and magnetic carriers transferred to the surface of the electrostatic latent image carrier;
An effective potential difference ΔVep (V) obtained by subtracting a developing bias voltage in the carrier transfer step from a surface potential formed on the surface of the electrostatic latent image carrier in the second charging step; The effective potential difference ΔVei (V) obtained by subtracting the developing bias voltage in the developing step from the surface potential formed on the surface of the body is expressed by the following equations (1) and (2):
| ΔVep |> | ΔVei | (1)
20 ≦ | ΔVep | − | ΔVei | ≦ 200 (2)
Means for controlling the applied voltage to be set in a range satisfying
An image forming apparatus comprising: A charging step of uniformly charging the surface of the electrostatic latent image carrier, an exposure step of exposing the surface of the electrostatic latent image carrier to form an electrostatic latent image, A developing step of visualizing the electrostatic latent image with the applied toner, a transfer step of transferring the toner image formed on the electrostatic latent image carrier by the visualization onto a transfer target, A cleaning step of bringing a cleaning unit into contact with the surface of the image carrier, and
As the toner, a toner whose charge polarity is the same polarity as the surface potential formed on the surface of the electrostatic latent image carrier and the developing bias voltage applied to the surface of the developer carrier by the charging step,
As the magnetic carrier, a magnetic carrier having a saturation magnetization of 45 to 55 emu / g and a magnetic carrier passing through a mesh having an opening of 30 μm in a proportion of 3 to 20% by weight is used,
The spontaneous transfer amount of the magnetic carrier from the surface of the developer carrier to the surface of the electrostatic latent image carrier in the developing step is determined by a series of image forming processing steps including the charging, exposure, development, transfer and cleaning of 1000 cycles. It is set to be 0.02-0.2 g when repeated, and
An image forming method, wherein the magnetic carrier transferred to the surface of the electrostatic latent image carrier is removed from the surface of the electrostatic latent image carrier by the cleaning means in the cleaning step.

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