JP3604904B2 - Contact charging method - Google Patents

Description

【００３５】
上記の結果より、角度θが３０°〜９０°の範囲で良好な画像が得られ、特に角度θが６３°の付近、すなわち隘狭部３の容積が最大になる付近で安定した画像が得られることが判った。
【００３６】
［実施例２］
炭酸ガスに代えてアルゴン（Ａr）ガスを使用し、実施例１と同様にして画像形成を行ったところ、やはり角度θが６３°の付近で良好な画像が得られた。これにより、炭酸ガスの代りにアルゴンガスを炭酸ガスＧに使用できることが判った。
【００３７】
［実施例３］
第２の実施の形態の装置構成において、径４０ｍｍφの感光体ドラム１と径１５ｍｍφの帯電ローラ２の長さを同じにして両端を揃え、帯電ローラ２の両端面に径２０ｍｍφの円盤状の遮蔽部材５を固定した。隘狭部３内に炭酸ガスを静かに注入しながら、感光体ドラム１と帯電ローラ２との間の微少空間中にコロナ放電を発生させて感光体ドラム１を帯電させた後、露光、現像、転写、定着の一連の作像工程を実施して画像を形成した。その結果、遮蔽部材５を設けなかったときと比較すると、炭酸ガスの流出量は大幅に減少し、良好な画像形成を長期行えるようになった。
【００３８】
［実施例４］
第３の実施の形態の装置構成において、径４０ｍｍφの感光体ドラム１と、径１５ｍｍφの帯電ローラ２と、径１０ｍｍφの回転体４とを使用し、これら３つの回転体により囲まれる密閉空間に遮蔽部材９に設けた吸排気口から炭酸ガスを流し込んで充填し、３０ｍｍＨｇ程度に減圧して、感光体ドラム１、帯電ローラ２、及び回転体４に電圧を印加して内部でコロナ放電を発生させて感光体ドラム１を帯電させた後、露光、現像、転写、定着の一連の作像工程を実施して画像を形成した。
【００３９】
［実施例５］
実施例４と同じ装置で放電雰囲気ガスによる置換を行わず、密閉空間内を空気のまま減圧した状態で、感光体ドラム１を帯電させた後、一連の作像工程を実施して画像を形成した。
【００４０】
［比較例］
実施例４、５と同じ装置で放電雰囲気ガスによる置換を行わず、密閉空間内を空気のまま減圧せずに感光体ドラム１を帯電させた後、一連の作像工程を実施して画像を形成した。以上の結果、比較例では実施例４、５と同じ印加電圧では得られた画像にかぶりが生じ、印加電圧を上げて良好な画質を得られるようにすると、オゾンの異臭はしないもののオゾン濃度が実施例４、５の場合の１０倍以上増加した。これに対し実施例４、５では安定して良好な画像が得られた。
【００４１】
【発明の効果】
以上説明したように、本発明は以下のような優れた効果を奏する。
請求項１に記載の発明では、電子写真方式の画像形成プロセスである帯電、転写、もしくは除電のうちの少なくとも一つのプロセスをコロナ放電を利用して行う画像形成装置において、被帯電部材の表面に帯電部材の帯電部を順次接触させ、前記被帯電部材と前記帯電部材の帯電部との間の微少空間中に発生する放電により前記被帯電部材の表面に電荷を供給する接触帯電方法において、前記被帯電部材と前記帯電部材とが接触することにより形成される隘狭部に空気よりも比重の大きい炭酸ガスを滞留させた状態で前記放電を発生させるようにしたことにより、コロナ放電発生箇所から炭酸ガスが逃げ出さないようにするために装置構成を複雑化することなく、コロナ放電発生箇所に炭酸ガスを供給して、コロナ放電によるオゾンやＮＯxの発生を防止しつつ被帯電部材を帯電させることができる。また、炭酸ガスを用いるようにしたことにより、コロナ放電によるオゾンやＮＯxの発生を効果的に防止しつつ被帯電部材を帯電させることができる。また、炭酸ガスは空気中に多く存在し比較的容易に採取できるガスであり、廉価であるため、その他のガスを使用した場合と比較して運転コストを低減できる。また、コロナ放電によって二次的に炭酸ガスが発生することはないので、地球温暖化など地球環境に与える影響は少ない。
【００４２】
また、請求項２に記載の発明では、請求項１に記載の方法において、前記被帯電部材と前記帯電部材はどちらも円筒状若しくは円柱状の部材であるとともに、水平方向に互いに平行に延びるそれぞれの中心軸線回りに回転する部材であり、且つ、前記被帯電部材の回転中心と前記帯電部材の回転中心とを結ぶ直線が被帯電部材の回転中心を鉛直方向に通過する直線となす角度が３０°〜９０°となるように配置されているので、両部材同士が接触することにより形成される隘狭部への炭酸ガスの滞留量を十分に確保し、コロナ放電を良好に発生させることができるので、被帯電部材を良好に帯電させることができる。
【００４３】
また、請求項３に記載の発明では、請求項２に記載の方法において、前記被帯電部材の半径をＲ、前記帯電部材の半径をｒ、前記角度をθとしたとき、これらの値の間に
θ＝ｃｏｓ^-1（（Ｒ−ｒ）／（Ｒ＋ｒ））
なる式で表される関係がほぼ成立するようにしたことにより、形成される隘狭部への炭酸ガスの滞留量を最大にすることができるので、コロナ放電ひいては被帯電部材の帯電をより良好に実現できる。
【００４４】
また、請求項４〜７に記載の発明では、電子写真方式の画像形成プロセスである帯電、転写、もしくは除電のうちの少なくとも一つのプロセスをコロナ放電を利用して行う画像形成装置において、被帯電部材の表面に帯電部材の帯電部を順次接触させ、前記被帯電部材と前記帯電部材の帯電部との間の微少空間中に発生する放電により前記被帯電部材の表面に電荷を供給する接触帯電方法において、前記被帯電部材と前記帯電部材とが接触することにより形成される窪み状の隘狭部に空気よりも比重の大きい炭酸ガスを滞留させるとともに、当該隘狭部からの炭酸ガスの流出を前記被帯電部材又は前記帯電部材の両端部に設けた遮蔽部材で防ぎつつ前記放電を発生させるようにしたので、前記遮蔽部材の外周縁が部前記被帯電部材の軸芯に接触することがなく、前記遮蔽部材の外周縁が前記帯電部材の頂点を含む水平面が前記被帯電部材の端部外縁と交差する点に達しているので、前記遮蔽部材を設けたことにより前記帯電部材の回転が妨げられることはなく、前記隘狭部の両端から炭酸ガスが流出するのを防ぐことができ、炭酸ガスの使用効率を高めることができる。
【図面の簡単な説明】
【図１】本発明の接触帯電方法の第１の実施の形態を示す画像形成装置の要部概略構成図である。
【図２】図１中に示す隘狭部の容積が最大となる場合を示した説明図である。
【図３】本発明の接触帯電方法の第２の実施の形態を示す画像形成装置の要部の構成を示した概略側面図である。
【図４】図３に示した画像形成装置の要部を矢印Ｘ方向から見た正面図である。
【図５】本発明の接触帯電方法の第３の実施の形態を示す画像形成装置の要部の構成を示した概略側面図である。
【図６】図５に示した画像形成装置の要部を矢印Ｘ方向から見た正面図である。
【符号の説明】
１ 感光体ドラム（被帯電部材）
２ 帯電ローラ（帯電部材）
３ 隘狭部
４ ガス供給管
５ 遮蔽部材
６ 回転体
７ 遮蔽部材
Ｇ 炭酸ガス
Ｏ₁ 回転中心
Ｐ 接触点
Ｑ₁ 頂点
Ｒ 感光体ドラム１の半径
ｒ 帯電ローラの半径[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for charging a member to be charged such as a photoreceptor in an electrophotographic image forming apparatus, and more particularly to a contact charging method.
[0002]
[Prior art]
Image forming apparatuses such as copiers, printers, and facsimile machines uniformly charge the surface of a photoconductor whose resistance changes depending on the degree of light irradiation, and irradiate the surface of the photoconductor with a laser beam or the like to output an image. After the electrostatic latent image is formed in accordance with the image forming method, a charged toner (charge carrier) is attached to the electrostatic latent image and developed, and the toner image is transferred to a charged transfer body such as paper. There is a method in which an image is formed by a series of so-called electrophotographic processes in which a toner image on a transfer member is fixed by heat and pressure after the toner image is removed from the photoreceptor by removing static electricity. After the above series of processes, the toner remaining on the surface of the photoconductor is removed. Then, the surface of the photoreceptor is once charged and then uniformly charged for the next image formation. The electrophotographic method utilizes the movement of electric charges in each process of charging, development, transfer, and static elimination. As methods for generating electric charges, there are corona discharge method, contact friction charging method, contact charge injection method, and the like. Has been used. Among them, the most common method is a corona discharge method.
[0003]
In the corona discharge method, a corona discharge is generated between electrodes by applying a strong electric field between an electrode using a fine wire or a needle and an opposing electrode, and ions generated by the discharge are applied to a charged member such as a photoconductor. This is a method in which charge is supplied by attaching. This method has a simple principle and a very simple apparatus configuration for implementing the method. However, since corona discharge is performed in the air, oxygen occupying 20% of the air component is ionized and ozone (O_Three) Occurs. O_ThreeIs a molecule that is required above the atmosphere to suppress the amount of ultraviolet rays and the like incident from the sun to the ground, but is a harmful substance in the office environment and needs to be suppressed. The contact frictional charging method and the contact charge injection method are applied to a developing roller and a charging roller.However, since the developing roller and the charging roller come into contact with the surface of the photoreceptor which is a member to be charged when the roller is stopped, a rubber layer of the roller is used. The low molecular weight component contained in the photoreceptor precipitates and migrates to the photoreceptor, thereby causing contamination of the photoreceptor and eventually causing an abnormality in an image. Therefore, recently, the surface of the charging member is made to have a high resistance, and the charging portion of the charging member is sequentially brought into contact with the surface of the member to be charged such as a photoconductor, and before and after the contact between the surface of the charging member and the charging portion of the charging member. A contact charging method has been employed in which a corona discharge is generated in a minute space to uniformly charge the entire surface of the member to be charged.
[0004]
[Problems to be solved by the invention]
However, in the case of the contact charging method as well, oxygen in the air is ionized and corona is inevitably generated because corona discharge is utilized. The knock component has a hygroscopic property, and if this component adheres to the photoreceptor, an abnormal image called image deletion occurs, and it adheres to the photoreceptor and the charging roller, and when the two come into contact with each other, the low-molecular component from the charging roller is transferred to the photoreceptor. It has been found that the movement and adhesion cause white spots after the stop and restart. Therefore, development of a discharge atmosphere gas that does not generate ozone has been desired.
[0005]
As one example, Japanese Patent Application Laid-Open No. Sho 60-95459 proposes a method using a gas having a lower oxygen concentration than air. However, although simply reducing the oxygen concentration has the effect of reducing the amount of ozone generated, it does not completely prevent ozone generation, and the amount of corona discharge current varies depending on the type of gas. The potential fluctuates and the image density varies. For this reason, there is a problem that the device configuration is complicated, for example, it is necessary to attach a gas separation filter. Therefore, it is necessary to create a discharge atmosphere that does not contain oxygen at all or that does not generate ozone by corona discharge even if it contains oxygen. Nitrogen (N_Two) A gas is conceivable, but nitrogen is quickly diffused into the air and dissipated because the gas density is close to that of oxygen. Therefore, in order to constantly maintain a pure nitrogen atmosphere, a special device and a nitrogen supply device are required. Also, as described in Japanese Patent Application Laid-Open No. 60-95459, NOx is generated by corona discharge of nitrogen, which causes a significant deterioration of the charging ability of the photoreceptor, such as an increase in hygroscopicity. , NOx should be avoided. Other familiar gases include water vapor (H_TwoO), hydrogen (H_Two), Helium (He), neon (Ne), propane (C_ThreeH₈), Methane (CH_Four ), But fire-hazardous ones cannot be used, and those that are not gaseous at normal temperature cannot be used stably. In addition, if a gas that is lighter than air is used even if it is a gas that does not generate ozone, take measures such as installing an umbrella-shaped container so that the gas does not escape from the location where corona discharge occurs, or supplying gas constantly to the location where corona discharge occurs. Need to be taken.
[0006]
The present invention has been made in view of the above circumstances, and its purpose is toIn an image forming apparatus that performs at least one process of charging, transferring, or discharging, which is an electrophotographic image forming process, using corona discharge,A contact charging method that can charge a member to be charged while preventing the generation of ozone and NOx due to corona discharge without complicating the device configuration in order to prevent the non-ozone-generating gas from escaping from the corona discharge generation location. Is to provide.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is an image forming apparatus that performs at least one of charging, transfer, and charge elimination, which is an electrophotographic image forming process, using corona discharge. In the above, the charging portion of the charging member is sequentially brought into contact with the surface of the charging member, and the electric charge is generated on the surface of the charging member by a discharge generated in a minute space between the charging member and the charging portion of the charging member. In the contact charging method for supplying, the discharge is generated in a state where carbon dioxide gas having a specific gravity larger than that of air is retained in a narrow portion formed by the contact between the charged member and the charging member. .
[0008]
Since gas having a larger specific gravity than air flows naturally to a lower portion, as described above, carbon dioxide gas having a large specific gravity is used, and is formed by contacting the member to be charged and the charging member. The carbon dioxide gas is supplied to the location where corona discharge occurs, and the ozone generated by corona discharge is supplied to the location where corona discharge occurs without complicating the device configuration in order to prevent the carbon dioxide gas from escaping from the location where corona discharge occurs by staying in the narrow part. The member to be charged can be charged while preventing generation of NOx and NOx. In addition, as a non-ozone generating gas, a gas having a molecular structure containing no oxygen is optimal, and carbon dioxide gas contains oxygen in its molecular structure, but this molecule is extremely stable and is extinguished in the event of a fire. It is used as an agent. Further, it does not dissociate and generate oxygen at the energy of the normal corona discharge level, but has the property of being sufficiently ionized and ionized. Therefore, by using carbon dioxide gas as the non-ozone generating gas, the member to be charged can be charged while effectively preventing generation of ozone and NOx due to corona discharge.
[0009]
According to a second aspect of the present invention, based on the premise of the first aspect, both the charged member and the charging member are cylindrical or columnar members, and are parallel to each other in a horizontal direction. And a straight line connecting the rotation center of the charged member and the rotation center of the charging member is a straight line passing through the rotation center of the charging member in the vertical direction. They are arranged so that the angle is 30 ° to 90 °.
[0010]
When both the member to be charged and the charging member are cylindrical or columnar members, the members are arranged in a positional relationship that satisfies the angle range according to claim 2 so that both members come into contact with each other. By doing so, a sufficient amount of carbon dioxide gas stays in the narrow portion formed by this process, and corona discharge can be satisfactorily generated, so that the member to be charged can be satisfactorily charged.
[0011]
Further, the invention described in claim 3 is the same as the invention described in claim 2.MethodIn the above, when the radius of the member to be charged is R, the radius of the charging member is r, and the angle is θ, between these values
θ = cos^-1((R−r) / (R + r)) Equation (1)
The relationship represented by the following equation is substantially established.
[0012]
When both the member to be charged and the charging member are cylindrical or columnar members, the relationship between the radii R, r of the two members and the angle θ that determines the positional relationship between the two members is formulated as described above. By designing the device so as to satisfy this equation, the volume of the narrow portion formed above the contact portion between the two members is maximized. Accordingly, the amount of carbon dioxide gas retained in the narrow portion can be maximized, so that corona discharge can be more favorably generated and the member to be charged can be more favorably charged.
[0013]
According to a fourth aspect of the present invention, there is provided an image forming apparatus in which at least one of charging, transfer, and charge elimination, which is an electrophotographic image forming process, is performed using corona discharge. A contact charging method of sequentially contacting a charging portion of a charging member on a surface and supplying a charge to a surface of the charging member by a discharge generated in a minute space between the charged member and the charging portion of the charging member. While holding the carbon dioxide gas having a higher specific gravity than air in the hollow narrow portion formed by the contact between the charged member and the charging member, the outflow of carbon dioxide gas from the narrow portion is prevented. The discharge is generated while preventing the member to be charged or the shielding members provided at both ends of the charging member.
[0014]
According to a fifth aspect of the invention, based on the premise of the fourth aspect, the shielding member is fixed to both ends of the charged member or the charging member.
[0015]
According to a sixth aspect of the present invention, on the premise of the method of the fifth aspect, both the charged member and the charging member are cylindrical or columnar members, and are parallel to each other in a horizontal direction. The shielding member is a disk concentrically fixed to both ends of the charging member, and its outer peripheral edge is in contact with the axis of the member to be charged. Alternatively, a horizontal plane including the apex of the charging member may reach a point intersecting the outer edge of the end of the member to be charged.
[0016]
Further, the invention according to claim 7 is based on the premise of the method according to claim 6, wherein the radius of the charged member is R, the radius of the charging member is r, and the radius of the axis of the charged member is r. R ′, a radius of the shielding member is r ″, and an angle between a straight line connecting the rotation center of the charged member and the rotation center of the charging member to a vertical line passing through the rotation center of the charged member is θ. , Between these values,
RR '+ r ≧ r " r / sin [ θ-cos ^-1 [ (1 + r / R) cos θ + r / R ]]
The following relationship is established.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[First Embodiment]
FIG. 1 is a schematic diagram of a main part of an image forming apparatus showing a contact charging method according to a first embodiment of the present invention. In FIG. 1, 1 is a photosensitive drum as a member to be charged, and 2 is a charging member as a charging member. The rollers are shown. In this apparatus, a charged charging roller 2 is rotated while being in contact with the surface of a photosensitive drum 1 rotating at a constant speed in a fixed direction, so that the surface of the photosensitive drum 1 and the surface (charging portion) of the charging roller 2 are rotated. By generating a corona discharge in the minute space between the photosensitive drums, a charge is supplied to the surface of the photosensitive drum 1 to be charged. At this time, carbon dioxide (CO 2) having a higher specific gravity than air is applied to a narrow portion 3 formed by the contact between the photosensitive drum 1 and the charging roller 2._Two) G is retained and corona discharge is generated in a carbon dioxide gas atmosphere. The carbon dioxide gas G is supplied from above into a narrow portion 3 through a gas supply pipe 4 from a gas supply source (not shown).
[0018]
The photosensitive drum 1 and the charging roller 2 are members that rotate around respective central axes extending parallel and horizontally to each other, and the rotation center O of the photosensitive drum 1 is₁With respect to each other and the vertex Q of the photosensitive drum 1₁, That is, the vertex Q of the photosensitive drum 1₁And rotation center O₁And a straight line l₁And the contact point P of each other and the vertex Q of the photosensitive drum 1₁And rotation center O₁And a straight line l_TwoAre arranged in a positional relationship such that the angle θ between them is 30 ° to 90 °. By arranging the photosensitive drum 1 and the charging roller 2 in such a positional relationship, the amount of carbon dioxide gas G retained in the narrow portion 3 formed by the contact between the photosensitive drum 1 and the charging roller 2 can be reduced. Sufficiently secured, and corona discharge can be satisfactorily generated without generating ozone.
[0019]
When the radius of the photosensitive drum 1 is R and the radius of the charging roller 2 is r, the volume of the narrowed portion 3 is the maximum when the relationship expressed by the above equation (1) is established with the angle θ. (See FIG. 2). This is the top Q of the photosensitive drum 1.₁And the top Q of the charging roller 2_TwoMeans that the heights are equal. Therefore, if the dimensions and arrangement of the respective members are set so that the above formulas are satisfied, by filling the narrow portion 3 with the carbon dioxide gas G, the stagnation amount of the carbon dioxide gas G can be maximized. At this time, the carbon dioxide gas G can be filled in the narrow portion 3 by allowing the carbon dioxide gas G to flow naturally from the gas supply pipe 4. When the discharge conditions change due to the dissipation or dilution of the carbon dioxide gas G, the carbon dioxide gas G is supplied to the outer peripheral surface of the charging roller 2 as a charging member. The method is simple. It is sufficient that carbon dioxide gas G is excessively supplied from the gas supply pipe 4 into the narrow portion 3 and slightly overflows.
[0020]
As described above, according to the present embodiment, it is possible to satisfactorily generate corona discharge and charge the photosensitive drum 1 while suppressing generation of ozone harmful to the office environment. A photoreceptor made of an organic material such as OPC is greatly deteriorated by ozone. However, since the generation of ozone is suppressed, the photoreceptor can be prevented from being deteriorated and the durability life can be extended. In addition, the use of the carbon dioxide gas G can prevent the generation of a knock (NOx), thereby preventing the occurrence of an abnormal image or the like due to the attachment of the knock component to the photoconductor.
[0021]
[Second embodiment]
FIG. 3 is a schematic side view showing a configuration of a main part of an image forming apparatus showing a second embodiment of the contact charging method of the present invention, and FIG. 4 is a view showing a main part of the image forming apparatus shown in FIG. It is the front view seen from the direction. In this apparatus, a charged charging roller 2 is rotated while being in contact with the surface of a photosensitive drum 1 rotating at a constant speed in a fixed direction, so that the surface of the photosensitive drum 1 and the surface (charging portion) of the charging roller 2 are rotated. By generating a corona discharge in the minute space between the photosensitive drums, a charge is supplied to the surface of the photosensitive drum 1 to be charged. At this time, carbon dioxide (CO 2) having a higher specific gravity than air is applied to a narrow portion 3 formed by the contact between the photosensitive drum 1 and the charging roller 2._Two) G is retained and corona discharge is generated in a carbon dioxide gas atmosphere. The carbon dioxide gas G is supplied from above into a narrow portion 3 through a gas supply pipe 4 from a gas supply source (not shown).
[0022]
The photosensitive drum 1 and the charging roller 2 are members that are fixed to respective shaft cores 6 and 7 that extend in parallel and horizontally with each other and that rotate respectively. The photosensitive drum 1 and the charging roller 2 have the same length, and a disc-shaped shielding member 5 is provided at both ends of the charging roller 2 to prevent carbon dioxide G from flowing out from both sides of the narrow portion 3. 2 and are fixed concentrically. The shielding member 5 does not have its outer peripheral portion in contact with the shaft core 6 of the photosensitive drum 1 and has a vertex Q of the charging roller 2._TwoAre designed to reach a point C where the horizontal plane including the edge crosses the outer edge of the end of the photosensitive drum 1.
[0023]
That is, the radius of the photosensitive drum 1 is R, the radius of the charging roller 2 is r, the radius of the axis 6 of the photosensitive drum 1 is R ′, the radius of the shielding member 5 is r ″, and the rotation center O of the photosensitive drum 1 is₁And the rotation center O of the charging roller 2_TwoAnd a straight line l_TwoIs the rotation center O of the photosensitive drum 1₁A straight line l passing vertically₁Is the angle between these values, the following inequality
R−R ′ + r ≧ r ″ r / sin [θ-cos−1 [(1 + r / R) cosθ + r / R]] (2)
Are set such that the following holds. If the dimensions of each part of the apparatus are set as described above, the provision of the shielding member 5 does not hinder the rotation of the charging roller 2, and the carbon dioxide G from both ends of the narrow part 3 is prevented. Since the outflow can always be prevented, the use efficiency of the carbon dioxide gas G can be increased.
[0024]
Further, the photosensitive drum 1 and the charging roller 2 are arranged in a positional relationship such that the angle θ is 30 ° to 90 °. By arranging the photosensitive drum 1 and the charging roller 2 in such a positional relationship, a sufficient amount of the carbon dioxide gas G stays in the narrow portion 3 and a corona discharge can be favorably generated without generating ozone. be able to. The volume of the narrow portion 3 becomes maximum when the relationship represented by the above equation (1) is established between the radius R of the photosensitive drum 1 and the radius r of the charging roller 2 and the angle θ. This is the top Q of the photosensitive drum 1.₁And the top Q of the charging roller 2_TwoMeans that the heights are equal. Therefore, if the dimensions and arrangement of the respective members are set so that this equation is satisfied, the maximum amount of the carbon dioxide gas G can be secured by filling the narrow portion 3 with the carbon dioxide gas G.
[0025]
At this time, the carbon dioxide gas G can be filled in the narrow portion 3 by allowing the carbon dioxide gas G to flow naturally from the gas supply pipe 4. When the discharge conditions change due to the dissipation or dilution of the carbon dioxide gas G, the carbon dioxide gas G is supplied to the outer peripheral surface of the charging roller 2 as a charging member. The method is simple. It is sufficient that carbon dioxide gas G is excessively supplied from the gas supply pipe 4 into the narrow portion 3 and slightly overflows.
[0026]
As described above, according to the present embodiment, it is possible to satisfactorily generate corona discharge and charge the photosensitive drum 1 while suppressing generation of ozone harmful to the office environment. A photoreceptor made of an organic material such as OPC is greatly deteriorated by ozone. However, since the generation of ozone is suppressed, the photoreceptor can be prevented from being deteriorated and the durability life can be extended. Further, since the generation of NOx can be prevented by using the carbon dioxide gas G, it is possible to prevent the occurrence of an abnormal image or the like due to the NOx component adhering to the photoconductor. In the above-described embodiment, the shielding members that prevent the carbon dioxide gas G from flowing out of the narrow portion 3 are provided at both ends of the charging roller 2, but may be provided at both ends of the photosensitive drum 1. However, in this case, the shielding member does not contact the shaft core 7 of the charging roller 2 and the vertex Q of the charging roller 2_TwoNeed to be dimensioned to reach
[0027]
[Third Embodiment]
FIG. 5 shows a second embodiment of the contact charging method of the present invention.36 is a schematic side view showing the configuration of the main part of the image forming apparatus showing the embodiment, and FIG. 6 is a front view of the main part of the image forming apparatus shown in FIG. This apparatus rotates a charged roller 2 in the same direction (arrow B direction) as the photosensitive drum 1 while contacting the surface of the photosensitive drum 1 rotating at a constant speed in a fixed direction (arrow A direction), By generating corona discharge in a minute space between the surface of the photosensitive drum 1 and the surface (charging portion) of the charging roller 2, a charge is supplied to the surface of the photosensitive drum 1 and charged. At this time, a corona discharge is generated in a state where the discharge atmosphere gas G is retained in the upper narrow portion 3a formed by the contact between the photosensitive drum 1 and the charging roller 2.
[0028]
The photoconductor drum 1 and the charging roller 2 are members that are fixed to respective shaft cores 7 and 8 extending in parallel and horizontally and that are forcibly driven to rotate. A rotating body 8 is provided which rotates in contact with the drum 1 and the charging roller 2. Further, shielding members 9 are provided at both ends of the narrow portion 3a to prevent the discharge atmosphere gas G from flowing out from both sides. By providing the rotating body 8 and the shielding member 9 in this manner, the narrow portion 3a is sealed, so that ozone and NOx are not released to the outside from the narrow portion 3a, and the use of the discharge atmosphere gas G is prevented. Efficiency can be increased. Further, since the rotating body 8 rotates in contact with the photosensitive drum 1 and the charging roller 2, no new driving unit is required.
[0029]
The potential of the rotating body 8 is set to be equal to or lower than the potential of the charging portion of the charging roller 2 and higher than the potential of the surface of the photosensitive drum 1. By maintaining such a potential relationship, the occurrence of discharge from the charging roller 2 to the rotating body 8 can be suppressed, and even if such a discharge occurs, the photosensitive drum 1 is not affected by the potential of the rotating body 8. Since charging can be prevented, discharge from the charging roller 2 to the photosensitive drum 1 can be stably generated, and the photosensitive drum 1 can be charged stably. The discharge atmosphere gas G is supplied into the narrow portion 3a through a gas supply pipe (not shown) provided through the shielding member 9. An exhaust pipe (not shown) for forcibly exhausting the gas in the narrow portion 3a is connected to the shielding member 9, and the pressure in the narrow portion 3a is reduced by exhausting the gas. The discharge atmosphere gas G can be introduced into 3a. Since the pressure in the narrow portion 3a can be reduced in this manner, a discharge easily occurs between the surface of the photosensitive drum 1 and the surface of the charging roller 2, so that the charging process can be performed very efficiently.
[0030]
The pressure in the narrow portion 3a can be determined based on the well-known Paschen's law. That is, according to Paschen's law, the discharge starting voltage V is a function of the product P · d of the pressure of the atmosphere and the distance d between the electrodes, and V increases in both the decreasing direction and the increasing direction of P · d. , Take a minimum value at a certain value of P · d. Since the pressure P and the distance d have an inverse proportional relationship (reciprocity law) with respect to the discharge starting voltage V, the distance d increases as the pressure P decreases. Therefore, the pressure P may be determined according to the distance d to be secured when causing corona discharge. For example, taking air as an example, the discharge start voltage V = 310 [V] is obtained when P · d = 5 mm · mmHg, so if the distance d is to be 5 mm, the pressure P should be 1 mmHg. Just fine.
[0031]
As described above, according to the present embodiment, the upper narrow portion 3a formed by the contact between the photosensitive drum 1 and the charging roller 2 is sealed, and the discharge atmosphere gas G is retained in the sealed space. Since the corona discharge is generated in the discharged state, even if air or oxygen is used as the discharge atmosphere gas G, ozone does not flow out. However,Over timeSince it is conceivable that the airtightness of the narrow portion 3a is reduced, a gas that does not generate ozone by corona discharge, such as carbon dioxide (CO_Two), Argon (Ar) gas or the like is desirably used. Since the generation of NOx can be prevented by using a carbon dioxide gas or an argon gas, it is possible to prevent the occurrence of an abnormal image due to the NOx component adhering to the photoreceptor.
[0032]
In the above-described embodiment, the discharge atmosphere gas G is made to stay in the closed space in which the upper narrow portion 3a is sealed. Even if G is retained, the same effect as in the above embodiment can be exerted. In the above example, the photosensitive drum 1 and the charging roller 2 rotate in the same direction. However, for example, the charging roller 2 may be rotated in the opposite direction (the direction of the arrow B '). In that case, it is desirable that the rotating body 5 be forcibly rotated in one direction.
[0033]
【Example】
[Example 1]
In the apparatus configuration of the first embodiment, a photosensitive drum 1 having a diameter of 40 mmφ and a charging roller 2 having a diameter of 15 mmφ are used, and the positional relationship between them, that is, the angle θ is variously changed. The layout of the developing unit, the transfer unit, the fixing unit, and the like is slightly changed, and corona discharge is caused in the minute space between the photosensitive drum 1 and the charging roller 2 with the narrow portion 3 filled with carbon dioxide. After the generated photosensitive drum 1 was charged, a series of image forming steps of exposure, development, transfer, and fixing were performed to form an image. As a result, the results shown in Table 1 below were obtained.
[0034]
[Table 1]

[0035]
From the above results, a good image is obtained when the angle θ is in the range of 30 ° to 90 °, and in particular, a stable image is obtained near the angle θ of 63 °, that is, near the maximum volume of the narrow portion 3. It turned out to be.
[0036]
[Example 2]
When an image was formed in the same manner as in Example 1 except that argon (Ar) gas was used instead of carbon dioxide gas, a good image was obtained when the angle θ was around 63 °. This proved that argon gas could be used for carbon dioxide gas instead of carbon dioxide gas.
[0037]
[Example 3]
In the apparatus configuration of the second embodiment, the length of the photosensitive drum 1 having a diameter of 40 mmφ and the length of the charging roller 2 having a diameter of 15 mm are equal, and both ends thereof are aligned. The member 5 was fixed. After the corona discharge is generated in the minute space between the photosensitive drum 1 and the charging roller 2 while the carbon dioxide gas is gently injected into the narrow portion 3, the photosensitive drum 1 is charged, and then exposed and developed. An image was formed by performing a series of image forming steps of transfer, fixing and fixing. As a result, as compared with the case where the shielding member 5 was not provided, the outflow amount of carbon dioxide gas was significantly reduced, and good image formation could be performed for a long time.
[0038]
[Example 4]
In the apparatus configuration of the third embodiment, a photosensitive drum 1 having a diameter of 40 mm, a charging roller 2 having a diameter of 15 mm, and a rotating body 4 having a diameter of 10 mm are used, and a closed space surrounded by these three rotating bodies is used. Shielding member9A carbon dioxide gas is flowed in from the intake / exhaust port provided for charging, and the pressure is reduced to about 30 mmHg. After charging the body drum 1, a series of image forming steps of exposure, development, transfer, and fixing were performed to form an image.
[0039]
[Example 5]
After the photosensitive drum 1 is charged in the same apparatus as in the embodiment 4 without replacing with the discharge atmosphere gas and the pressure in the sealed space is reduced while keeping the air, a series of image forming steps are performed to form an image. did.
[0040]
[Comparative example]
In the same apparatus as in Examples 4 and 5, the photosensitive drum 1 was charged without performing the replacement with the discharge atmosphere gas and without depressurizing the air in the closed space, and a series of image forming processes was performed to form an image. Formed. As a result, in the comparative example, fogging occurs in the obtained images at the same applied voltage as in Examples 4 and 5, and when the applied voltage is increased so as to obtain good image quality, the ozone concentration is not increased, but the ozone concentration is reduced. The increase was at least 10 times that of Examples 4 and 5. In contrast, in Examples 4 and 5, good images were stably obtained.
[0041]
【The invention's effect】
As described above, the present invention has the following excellent effects.
According to the first aspect of the present invention, in an image forming apparatus that performs at least one of charging, transfer, and charge elimination, which is an electrophotographic image forming process, using corona discharge, The contact charging method of sequentially contacting the charging portions of the charging member and supplying charge to the surface of the charging member by discharge generated in a minute space between the charging member and the charging portion of the charging member, By causing the discharge to be generated in a state where carbon dioxide gas having a higher specific gravity than air is retained in a narrow portion formed by contact between the charged member and the charging member, from the corona discharge generation point Without complicating the device configuration to prevent carbon dioxide gas from escaping, supply carbon dioxide gas to the location where corona discharge occurs, and generate ozone and NOx by corona discharge. The member to be charged can be charged while preventing occurrence. In addition, by using carbon dioxide gas, the member to be charged can be charged while effectively preventing ozone and NOx from being generated by corona discharge. In addition, carbon dioxide gas is a gas which is present in the air in a large amount and can be collected relatively easily, and is inexpensive. Therefore, the operation cost can be reduced as compared with the case where other gases are used. In addition, since carbon dioxide gas is not generated secondary by corona discharge, the influence on the global environment such as global warming is small.
[0042]
According to a second aspect of the present invention, in the method according to the first aspect, each of the charged member and the charging member is a cylindrical or columnar member, and extends parallel to each other in a horizontal direction. The angle formed by a straight line connecting the rotation center of the charged member and the rotation center of the charging member to a straight line passing through the rotation center of the charged member in the vertical direction is 30. ° to 90 °, so that a sufficient amount of carbon dioxide gas stays in a narrow portion formed by contact between the two members can be sufficiently secured, and corona discharge can be favorably generated. Therefore, the member to be charged can be favorably charged.
[0043]
Further, in the invention according to claim 3, in the method according to claim 2, when the radius of the member to be charged is R, the radius of the charging member is r, and the angle is θ, a value between these values is obtained. To
θ = cos^-1((R−r) / (R + r))
By making the relationship expressed by the following formula substantially hold, the amount of carbon dioxide gas retained in the narrow portion to be formed can be maximized, so that the corona discharge and, consequently, the charging of the member to be charged can be improved. Can be realized.
[0044]
Further, in the image forming apparatus according to the present invention, at least one of charging, transferring, and discharging, which is an electrophotographic image forming process, is performed using corona discharge. Contact charging in which a charging portion of a charging member is sequentially brought into contact with the surface of the member and a charge is generated on a surface of the charging member by a discharge generated in a minute space between the charging member and the charging portion of the charging member. In the method, carbon dioxide gas having a higher specific gravity than air is retained in a concave narrow portion formed by contact between the charged member and the charging member, and carbon dioxide gas flows out of the narrow portion. The discharge is generated while preventing the charging member or the shielding members provided at both ends of the charging member, so that the outer peripheral edge of the shielding member is in contact with the axis of the charging member. The outer peripheral edge of the shielding member reaches a point where a horizontal plane including the apex of the charging member intersects with the outer edge of the end of the charged member, so that the charging member is provided by providing the shielding member. Of the carbon dioxide gas can be prevented from flowing out from both ends of the narrow portion, and the use efficiency of the carbon dioxide gas can be increased.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a main part of an image forming apparatus showing a first embodiment of a contact charging method of the present invention.
FIG. 2 is an explanatory diagram showing a case where the volume of a narrow portion shown in FIG. 1 is maximized.
FIG. 3 is a schematic side view illustrating a configuration of a main part of an image forming apparatus according to a second embodiment of the contact charging method of the present invention.
FIG. 4 is a front view of a main part of the image forming apparatus shown in FIG. 3 as viewed from an arrow X direction.
FIG. 5 is a schematic side view showing a configuration of a main part of an image forming apparatus showing a third embodiment of the contact charging method of the present invention.
FIG. 6 is a front view of a main part of the image forming apparatus shown in FIG.
[Explanation of symbols]
1 Photoconductor drum (member to be charged)
2 Charging roller (charging member)
3 Bottleneck
4 Gas supply pipe
5 Shielding member
6 rotating body
7 Shielding member
G carbon dioxide
O₁Rotation center
P contact point
Q₁vertex
R Radius of photosensitive drum 1
r radius of charging roller

Claims (7)

In an image forming apparatus that performs at least one process of charging, transferring, or discharging, which is an electrophotographic image forming process, using a corona discharge, a charging unit of a charging member is sequentially brought into contact with a surface of a member to be charged. A contact charging method for supplying a charge to the surface of the member to be charged by a discharge generated in a minute space between the member to be charged and a charging portion of the charging member,
Contact charging wherein the discharge is generated in a state where carbon dioxide gas having a specific gravity greater than that of air is retained in a narrow portion formed by contact between the charged member and the charging member. Method. Both the member to be charged and the charging member are cylindrical or columnar members, and are members that rotate about respective central axes extending in parallel with each other in the horizontal direction, and the rotation center of the member to be charged. 2. The device according to claim 1, wherein an angle between a straight line connecting the rotation center of the charging member and a straight line passing through the rotation center of the charged member in a vertical direction is 30 ° to 90 °. The contact charging method described above. When the radius of the member to be charged is R, the radius of the charging member is r, and the angle is θ, θ = cos ⁻¹ ((R−r) / (R + r)) between these values.
The contact charging method according to claim 2, wherein a relationship represented by the following formula is substantially established. In an image forming apparatus that performs at least one process of charging, transferring, or discharging, which is an electrophotographic image forming process, using a corona discharge, a charging unit of a charging member is sequentially brought into contact with a surface of a member to be charged. A contact charging method for supplying a charge to the surface of the member to be charged by a discharge generated in a minute space between the member to be charged and a charging portion of the charging member,
  While the carbon dioxide gas having a higher specific gravity than air stays in a narrow portion formed by the contact between the charged member and the charging member, the outflow of the carbon dioxide gas from the narrow portion causes the charged member or A contact charging method, wherein the discharge is generated while preventing the discharge with shielding members provided at both ends of the charging member. 5. The contact charging method according to claim 4, wherein the shielding member is fixed to both ends of the charged member or the charging member. Both the member to be charged and the charging member are cylindrical or columnar members, and are members that rotate around respective central axes that extend in parallel with each other in the horizontal direction, and the shielding member includes both ends of the charging member. The outer peripheral edge of the disk does not contact the axis of the member to be charged, and the horizontal plane including the apex of the charging member intersects with the outer edge of the end of the member to be charged. The contact charging method according to claim 5, wherein the contact point is reached. The radius of the member to be charged is R, the radius of the member to be charged is r, the radius of the axis of the member to be charged is R ′, the radius of the shielding member is r ″, the rotation center of the member to be charged and the charging member. When the angle between a straight line connecting the rotation center of the charged member and a straight line passing through the rotation center of the member to be charged in the vertical direction is θ, between these values,
R-R '+ r ≧ r " r / sin [ θ-cos ^-1 [ (1 + r / R) cos θ + r / R ]]
7. The contact charging method according to claim 6, wherein the following relationship is established.

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