JP2009015176A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of forming an image produced without scattering toner and releasing a recording medium from a conveyance member satisfactorily. <P>SOLUTION: This image forming device 1a includes a toner image forming means 2, a transfer means 3, a fixing means 4, a recording medium supply means 5, and a delivery means 6. A discharging means A is arranged on the downstream side of the transfer means 3 and on the upstream side of the fixing means 4 for the direction of conveyance of the recording medium by opposing to a face of the recording medium on which toner image is transferred and separating the discharging means A from the recording medium to discharge electricity of the toner having increased charge amount by the recording medium and the transfer on the recording medium. The voltage superimposed on a reverse polarity side to the toner image is applied on the discharging means A. When amplitude of alternating current of the voltage is Vp, the superimposed voltage is Vdc, and a discharging start voltage is Vs, this discharging means A satisfies the following expression (1): Vp>¾Vdc¾ +¾Vs¾. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  An image forming apparatus that forms an image using an electrophotographic system forms an image according to each process of charging, exposure, development, transfer, fixing, and cleaning. In the charging step, the surface of the photoreceptor, which is an image carrier for forming an electrostatic latent image, is charged. In the exposure step, an electrostatic latent image is formed on the surface of the photoconductor by irradiating the charged photoconductor surface with light according to image information. In the developing step, toner is attached to the formed electrostatic latent image, and a visible image (hereinafter referred to as “toner image”) visualized by the toner is formed on the surface of the photoreceptor. In the transfer process, the toner image formed on the surface of the photoreceptor is transferred onto the recording medium by an electric force. The transfer of the visible image to the recording medium may be performed via an intermediate transfer medium. In the fixing step, the toner image transferred onto the recording medium is melted by heat and fixed on the recording medium. In the cleaning step, for example, a cleaning member such as a cleaning blade scrapes off toner remaining on the surface of the photoconductor after the toner image is transferred, thereby cleaning the surface of the photoconductor.

  Recently, colorization technology in the electrophotographic system has rapidly developed, and full-color image forming apparatuses have been developed and provided to the market. The market for full-color image forming apparatuses is expanding with the spread of monochrome image forming apparatuses. In general, for color reproduction in a full-color image forming apparatus, three subtractive primary colors, yellow (y), magenta (m), and cyan (c), or black (b) are added to these three colors. Four color toners are used. As the color reproduction procedure, for each color y, m, c and b, the steps from charging, exposure, development and transfer in the image forming process are repeated for each color, and a plurality of color toners are formed on the recording medium. A full color toner image is formed by superimposing toner images composed of In the fixing step, the full color toner image is melted and fixed on the recording medium. Since the full-color toner image is melted in the fixing step and a plurality of color toners are mixed, the color is reproduced according to the principle of subtractive color mixing.

  In such full-color image formation, development is performed a plurality of times, a plurality of types of toner images having different colors are superimposed on the same recording medium in the transfer process, and a plurality of color toners are melted in the fixing process. To be fixed on the recording medium.

  Here, the toner charge amount of the toner image transferred onto the recording medium through the transfer process is larger than the toner charge amount before transfer due to the influence of the transfer electric field. In particular, the toner first transferred in full-color image formation passes through the transfer process a plurality of times, and thus is more affected by the transfer electric field. Further, in order to further improve the transferability, a charging means is provided before the transfer process, and the precharger system in which the toner charge amount before transfer is increased also increases the toner charge amount on the recording medium after transfer. .

  As described above, the toner having a large charge amount has a strong electric repulsion between the fixing roller that is frictionally charged at the fixing nip portion in the fixing process, and the image is scattered to reduce the image quality. There was a problem such as.

  On the other hand, since the recording medium that has undergone the transfer process is charged under the influence of the transfer electric field, it has poor peelability from the recording medium conveying member, causing jamming.

  By the way, with further improvements in various computer-related technologies, for example, as computer images become more precise, even in electrophotographic image forming apparatuses, it is possible to accurately detect minute shapes and subtle hue changes in computer images. Further, it is required to form a high-definition image that is vividly reproduced and comparable to a computer image. In order to meet this demand, for example, the toner has been reduced in particle size, and various studies have been made to produce a toner having a particle size of about 6 μm that is effective for high definition of images.

  Such a toner having a small particle diameter is useful for forming a high-definition image, but has a drawback of low transfer efficiency because it contains a large amount of fine powder. The small particle size toner has a larger specific surface area than, for example, a toner having a particle size larger than about 6 μm, and therefore has a strong non-electrostatic adhesion to the photoreceptor and the intermediate transfer medium. This makes it difficult for the toner having a small particle diameter to be transferred to the recording medium, and increases the amount of toner remaining on the photosensitive drum and the intermediate transfer medium after the transfer of the visible image to the recording medium.

  In view of such problems, proposals have been made to reduce the contact area between the photosensitive drum and the intermediate transfer medium and the toner and to improve the toner transfer efficiency by making the toner spherical. However, when the toner becomes nearly spherical, the transferability is improved, but the non-electrostatic adhesion is weakened. Therefore, particularly in the fixing process, the toner is in contact with the fixing roller that is frictionally charged at the fixing nip portion. There is a problem in that scattering is likely to occur because the electrical repulsive force of the steel is relatively strong.

  In view of this, an image forming apparatus in which a transfer belt and a fixing roller are provided with a static eliminating unit has been proposed. Since the neutralization of the toner transferred onto the recording medium is insufficient with the neutralization unit on the transfer belt alone, the second neutralization unit is provided on the fixing roller to suppress toner scattering. In addition, it has also been proposed to provide a neutralization unit between the fixing unit and the recording medium transport unit to simultaneously perform the separation of the recording medium and the neutralization of the fixing roller (see Patent Document 1, for example).

JP 2002-258627 A

  In the conventional image forming apparatus, there are problems such as an increase in cost and an increase in the amount of ozone generated due to the provision of two static elimination means. For example, when the charging polarity of the fixing roller is the same as the charging polarity of the recording medium charged with the opposite polarity of the toner, it becomes difficult to remove electricity from both the fixing roller and the recording medium, and the toner is scattered on the image. Or jams due to poor transport.

  An object of the present invention is to solve the conventional problems and provide an image forming apparatus capable of forming an image free from toner scattering and having good releasability of a recording medium from a conveying member.

The present invention comprises an image carrier that carries and conveys a toner image formed according to image information;
Transfer means for electrostatically transferring the toner image carried on the image carrier to a recording medium;
Neutralizing means for neutralizing the toner image transferred to the recording medium and the recording medium;
Fixing means for fixing the discharged toner image to the discharged recording medium,
The static elimination means includes
Provided on the downstream side of the transfer unit and the upstream side of the fixing unit in the conveyance direction of the recording medium;
The recording medium is disposed so as to face the side through which the toner image is transferred.
Apply a voltage superimposed on the opposite polarity side of the toner image,
The image forming apparatus is characterized in that when the amplitude of the AC voltage is Vp, the superimposed voltage is Vdc, and the discharge start voltage is Vs, the following expression (1) is satisfied.
Vp> | Vdc | + | Vs | (1)

In the present invention, the static eliminating means is
Apply a voltage superimposed on the opposite polarity side of the toner image,
When the amplitude of the AC voltage is Vp, the superimposed voltage is Vdc, and the discharge start voltage is Vs, the following equation (2) is satisfied.
0.5 <Vp− (| Vdc | + | Vs |) <2.5 (2)

  In the invention, it is preferable that an absolute value of a toner charge amount of the toner image that has been neutralized is 10 μC / g or more and 25 μC / g or less.

In the present invention, the transfer means comprises:
An intermediate transfer body that receives an intermediate transfer of a toner image carried on the image carrier at an intermediate transfer position and moves the toner image to a transfer position by moving in a predetermined direction while carrying the toner image;
And charging means for charging the toner image carried on the intermediate transfer member.

  In the present invention, the absolute value of the toner charge amount of the charged toner image is 20 μC / g or more and 40 μC / g or less.

  In addition, the present invention is characterized by using a toner having an average circularity of 0.955 or more and 0.975 or less.

  In addition, the present invention is characterized by using a toner having a volume average particle size of 4 μm or more and 8 μm or less.

  The present invention is characterized in that a toner containing 0.2 to 3 parts by weight of titanium oxide with respect to 100 parts by weight of the toner is used.

According to the present invention, an image forming apparatus carries an image carrier that carries and conveys a toner image formed according to image information, and electrostatically transfers the toner image carried on the image carrier to a recording medium. A transfer unit; a toner image transferred to the recording medium; a neutralizing unit that neutralizes the recording medium; and a fixing unit that fixes the neutralized toner image on the neutralized recording medium. Provided on the downstream side of the transfer unit and the upstream side of the fixing unit in the transport direction, and is disposed opposite the side of the recording medium on which the surface on which the toner image is transferred passes, and is superimposed on the opposite polarity side of the toner image When voltage is applied, the amplitude of the AC voltage is Vp, the superimposed voltage is Vdc, and the discharge start voltage is Vs, the following equation (1) is satisfied.
Vp> | Vdc | + | Vs | (1)

  The toner of the toner image transferred to the recording medium by the transfer means is charged under the influence of the transfer electric field. The fixing roller is charged by friction between the rollers. By providing a neutralization unit between the transfer unit and the fixing unit to sufficiently neutralize the toner, the electrical repulsive force between the toner and the fixing roller at the fixing nip portion is reduced, and the occurrence of toner scattering is reduced. Can be prevented. As a result, an image without toner scattering can be formed.

  Further, by applying an AC voltage satisfying the formula (1) to the charge eliminating means, not only the toner but also the recording medium charged to the opposite polarity side of the toner due to the influence of the transfer electric field can be discharged simultaneously. . This improves the peelability of the recording medium from the conveying member.

Further, according to the present invention, the neutralizing means applies a voltage superimposed on the opposite polarity side of the toner image, and when the amplitude of the AC voltage is Vp, the superimposed voltage is Vdc, and the discharge start voltage is Vs, It is preferable to satisfy the formula (2).
0.5 <Vp− (| Vdc | + | Vs |) <2.5 (2)

  Without excessively discharging the toner, the discharge amount having the same polarity as that of the toner can be increased, and the recording medium charged on the opposite polarity side of the toner can be sufficiently discharged at the same time. Thereby, the peelability of the recording medium from the conveying member is further improved.

  According to the invention, it is preferable that the absolute value of the toner charge amount of the discharged toner image is 10 μC / g or more and 25 μC / g or less. As a result, the electric repulsive force between the toner and the fixing roller is reduced, toner scattering at the fixing nip portion is reduced, and an image with good dot reproducibility can be formed. On the other hand, since an appropriate electrostatic adhesion force between the toner and the recording medium is maintained, it is possible to prevent the image from being disturbed during conveyance and to form a stable image.

  According to the invention, the transfer means receives the intermediate transfer of the toner image carried on the image carrier at the intermediate transfer position, and moves the toner image in the predetermined direction while carrying the toner image. It is preferable to include an intermediate transfer member conveyed to the intermediate transfer member and a charging unit for charging the toner image carried on the intermediate transfer member.

  Before transferring the toner image from the intermediate transfer member to the recording medium, the toner charge amount of the toner image is increased by the charging means, so that the transferability at the time of transfer is improved, so dot missing is eliminated and dot reproducibility is achieved. Will improve.

  Although the charging amount of the toner is increased by the charging unit, a neutralization unit is provided between the transfer unit and the fixing unit to sufficiently neutralize the toner, so that the electric charge between the toner and the fixing roller in the fixing nip portion can be obtained. The repulsive force can be reduced and the occurrence of toner scattering can be prevented. As a result, an image without toner scattering can be formed.

  According to the invention, the absolute value of the toner charge amount of the charged toner image is preferably 20 μC / g or more and 40 μC / g or less. This improves transferability and reduces missing dots.

  Further, according to the present invention, it is preferable to use a toner having an average circularity of 0.955 or more and 0.975 or less. This improves transferability and eliminates missing dots, thereby improving dot reproducibility.

  Further, according to the present invention, it is preferable to use a toner having a volume average particle diameter of 4 μm or more and 8 μm or less. This improves dot reproducibility. Further, it is possible to form a high-quality image with good fine line reproducibility.

  Further, according to the present invention, it is preferable to use a toner containing 0.2 to 3 parts by weight of titanium oxide with respect to 100 parts by weight of the toner. As a result, the toner resistance can be controlled, and transfer of charges generated by the charging means or the charge eliminating means can be made smooth so that the desired charge amount can be easily adjusted.

  FIG. 1 is a cross-sectional view schematically showing a configuration of an image forming apparatus 1a according to the first embodiment of the present invention.

  The image forming apparatus 1a is a multifunction machine having both a copying function, a printer function, and a facsimile function, and forms a full-color or monochrome image on a recording medium according to transmitted image information. That is, the image forming apparatus 1a has three types of printing modes, ie, a copier mode (copying mode), a printer mode, and a FAX mode. Operation input from an operation unit (not shown), personal computer, portable terminal device, information A print mode is selected by a control unit (not shown) in response to reception of a print job from an external device using a recording storage medium or a memory device. The image forming apparatus 1 a includes a toner image forming unit 2, a transfer unit 3, a fixing unit 4, a recording medium supply unit 5, and a discharge unit 6. Each member constituting the toner image forming unit 2 and some members included in the transfer unit 3 are black (b), cyan (c), magenta (m), and yellow (y) colors included in the color image information. In order to correspond to the image information, four each are provided. Here, each member provided by four according to each color is distinguished by attaching an alphabet representing each color to the end of the reference symbol, and when referring collectively, only the reference symbol is used.

  Here, the static eliminating means A of the present invention will be described. The neutralizing unit A is located downstream of the transfer unit 3 in the conveyance direction of the recording medium, upstream of the fixing unit 4, and opposite to the surface of the recording medium on which the toner image is transferred so as to be separated from the recording medium. The toner having a large charge amount is neutralized by being transferred to the recording medium and the recording medium. As the static elimination means A, a wire-type charger, a saw-tooth type charger, an ion generator, or the like can be used, but the invention is not particularly limited thereto.

A voltage superimposed on the side opposite to the toner image is applied to the charge removal means A. When the amplitude of the AC voltage is Vp, the superimposed voltage is Vdc, and the discharge start voltage is Vs, the following equation (1) is obtained. Fulfill.
Vp> | Vdc | + | Vs | (1)

  The toner of the toner image transferred to the recording medium by the transfer means 3 is charged under the influence of the transfer electric field. The fixing roller is charged by friction between the rollers. A neutralization unit A is provided between the transfer unit 3 and the fixing unit 4 to sufficiently neutralize the toner, thereby reducing the electric repulsive force between the toner and the fixing roller in the fixing nip portion. Can be prevented. As a result, an image without toner scattering can be formed.

Further, by applying an AC voltage satisfying the formula (1) to the charge eliminating means A, not only the toner but also the recording medium charged to the opposite polarity side of the toner due to the influence of the transfer electric field can be discharged simultaneously. it can. This improves the peelability of the recording medium from the conveying member.
Further, it is preferable to apply an AC voltage satisfying the following formula (2) to the static elimination means A.
0.5 <Vp− (| Vdc | + | Vs |) <2.5 (2)

  Without excessively discharging the toner, the discharge amount having the same polarity as that of the toner can be increased, and the recording medium charged on the opposite polarity side of the toner can be sufficiently discharged at the same time. Thereby, the peelability of the recording medium from the conveying member is further improved.

  In addition, the absolute value of the toner charge amount of the discharged toner image is preferably 10 μC / g or more and 25 μC / g or less. As a result, the electric repulsive force between the toner and the fixing roller is reduced, toner scattering at the fixing nip portion is reduced, and an image with good dot reproducibility can be formed. On the other hand, since an appropriate electrostatic adhesion force between the toner and the recording medium is maintained, it is possible to prevent the image from being disturbed during conveyance and to form a stable image.

  When the absolute value of the toner charge amount is less than 10 μC / g, the electrostatic adhesion between the toner and the recording medium is reduced by discharging the toner, and the image is disturbed during conveyance. When the absolute value of the toner charge amount exceeds 25 μC / g, toner scattering occurs due to electrical repulsion between the toner and the fixing roller.

  Here, the toner charge amount is obtained by sucking the toner present on the recording medium after passing through the charge eliminating means A using a charge amount measuring device (trade name: 210HS-2A, manufactured by Trek Japan Co., Ltd.). The toner charge amount Q / M (μC / g) can be obtained by dividing the charge amount Q (μC) of toner by the suction toner weight M (g).

  The toner image forming unit 2 includes a photosensitive drum 11, a charging unit 12, an exposure unit 13, a developing unit 14, and a cleaning unit 15. The charging unit 12, the developing unit 14, and the cleaning unit 15 are arranged around the photosensitive drum 11 in this order. The charging unit 12 is disposed below the developing unit 14 and the cleaning unit 15 in the vertical direction.

  The photosensitive drum 11 is supported by a driving unit (not shown) so as to be rotatable around an axis, and includes a conductive substrate (not shown) and a photosensitive layer formed on the surface of the conductive substrate. The conductive substrate can take various shapes, such as a cylindrical shape, a columnar shape, or a thin film sheet shape. Among these, a cylindrical shape is preferable. The conductive substrate is formed of a conductive material. As the conductive material, those commonly used in this field can be used. For example, metals such as aluminum, copper, brass, zinc, nickel, stainless steel, chromium, molybdenum, vanadium, indium, titanium, gold, platinum, etc. A conductive layer made of one or more of aluminum, aluminum alloy, tin oxide, gold, indium oxide and the like is formed on a film-like substrate such as two or more alloys, synthetic resin film, metal film, paper, etc. And a resin composition containing a conductive film, conductive particles, or a conductive polymer. In addition, as a film-form base | substrate used for an electroconductive film, a synthetic resin film is preferable and a polyester film is especially preferable. Moreover, as a formation method of the electroconductive layer in an electroconductive film, vapor deposition, application | coating, etc. are preferable.

  The photosensitive layer is formed, for example, by laminating a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material. In that case, it is preferable to provide an undercoat layer between the conductive substrate and the charge generation layer or the charge transport layer. By providing an undercoat layer, the scratches and irregularities present on the surface of the conductive substrate are coated to smooth the surface of the photosensitive layer, preventing deterioration of the chargeability of the photosensitive layer during repeated use, at low temperature or low humidity The advantage of improving the charging characteristics of the photosensitive layer under the environment can be obtained. Further, a laminated photoreceptor having a three-layer structure having a high durability and having a photoreceptor surface protective layer as the uppermost layer may be used.

  The charge generation layer is mainly composed of a charge generation material that generates a charge when irradiated with light, and contains a known binder resin, plasticizer, sensitizer and the like as necessary. As the charge generation material, those commonly used in this field can be used. Phthalocyanine pigments such as metal-free phthalocyanine, squalium dye, azulenium dye, thiapyrylium dye, carbazole skeleton, styryl stilbene skeleton, triphenylamine skeleton, dibenzothiophene skeleton, oxadiazole skeleton, fluorenone skeleton, bis stilbene skeleton, distyryl oxa And azo pigments having a diazole skeleton or a distyrylcarbazole skeleton. Among these, metal-free phthalocyanine pigments, oxotitanyl phthalocyanine pigments, bisazo pigments containing a fluorene ring or a fluorenone ring, bisazo pigments composed of aromatic amines, trisazo pigments, etc. have a high charge generating ability and are highly sensitive photosensitive layers. Suitable for getting. One type of charge generating material can be used alone, or two or more types can be used in combination. The content of the charge generation material is not particularly limited, but is preferably 5 to 500 parts by weight, more preferably 10 to 200 parts by weight with respect to 100 parts by weight of the binder resin in the charge generation layer. As the binder resin for the charge generation layer, those commonly used in this field can be used. For example, melamine resin, epoxy resin, silicone resin, polyurethane, acrylic resin, vinyl chloride-vinyl acetate copolymer resin, polycarbonate, phenoxy resin , Polyvinyl butyral, polyarylate, polyamide, polyester and the like. Binder resin can be used individually by 1 type, or can use 2 or more types together as needed.

  The charge generation layer generates charge by dissolving or dispersing appropriate amounts of charge generation materials, binder resins and, if necessary, plasticizers and sensitizers in an appropriate organic solvent capable of dissolving or dispersing these components. It can be formed by preparing a layer coating solution, applying this charge generation layer coating solution to the surface of the conductive substrate and drying. The film thickness of the charge generation layer thus obtained is not particularly limited, but is preferably 0.05 to 5 μm, more preferably 0.1 to 2.5 μm.

  The charge transport layer laminated on the charge generation layer has a charge transport material having the ability to accept and transport charges generated from the charge generation material and a binder resin for the charge transport layer as essential components, and if necessary Contains known antioxidants, plasticizers, sensitizers, lubricants and the like. As the charge transport material, those commonly used in this field can be used, for example, poly-N-vinylcarbazole and derivatives thereof, poly-γ-carbazolylethyl glutamate and derivatives thereof, pyrene-formaldehyde condensation product and derivatives thereof, Polyvinylpyrene, polyvinylphenanthrene, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, 9- (p-diethylaminostyryl) anthracene, 1,1-bis (4-dibenzylaminophenyl) propane, styrylanthracene, styrylpyrazoline, pyrazoline Derivatives, phenylhydrazones, hydrazone derivatives, triphenylamine compounds, tetraphenyldiamine compounds, triphenylmethane compounds, stilbene compounds, 3-methyl-2-benzothiazoline -Donating substances such as azine compounds, fluorenone derivatives, dibenzothiophene derivatives, indenothiophene derivatives, phenanthrenequinone derivatives, indenopyridine derivatives, thioxanthone derivatives, benzo [c] cinnoline derivatives, phenazine oxide derivatives, tetracyano Examples include electron-accepting substances such as ethylene, tetracyanoquinodimethane, promanyl, chloranil, and benzoquinone. The charge transport materials can be used alone or in combination of two or more. The content of the charge transport material is not particularly limited, but is preferably 10 to 300 parts by weight, more preferably 30 to 150 parts by weight with respect to 100 parts by weight of the binder resin in the charge transport material. As the binder resin for the charge transport layer, those commonly used in this field and capable of uniformly dispersing the charge transport material can be used. For example, polycarbonate, polyarylate, polyvinyl butyral, polyamide, polyester, polyketone, epoxy resin, polyurethane , Polyvinyl ketone, polystyrene, polyacrylamide, phenol resin, phenoxy resin, polysulfone resin, and copolymer resins thereof. Among these, in consideration of film formability, wear resistance of the resulting charge transport layer, electrical characteristics, etc., polycarbonate containing bisphenol Z as a monomer component (hereinafter referred to as “bisphenol Z type polycarbonate”), bisphenol Z type polycarbonate, A mixture with another polycarbonate is preferred. Binder resin can be used individually by 1 type, or can use 2 or more types together.

  The charge transport layer preferably contains an antioxidant together with the charge transport material and the binder resin for the charge transport layer. As the antioxidant, those commonly used in this field can be used, and examples thereof include vitamin E, hydroquinone, hindered amine, hindered phenol, paraphenylenediamine, arylalkane and derivatives thereof, organic sulfur compounds, and organic phosphorus compounds. It is done. One antioxidant can be used alone, or two or more antioxidants can be used in combination. The content of the antioxidant is not particularly limited, but is 0.01 to 10% by weight, preferably 0.05 to 5% by weight, based on the total amount of components constituting the charge transport layer. The charge transport layer is dissolved or dispersed in a suitable organic solvent that can dissolve or disperse these components in an appropriate amount such as a charge transport material and a binder resin, and if necessary, an antioxidant, a plasticizer, and a sensitizer. The charge transport layer coating liquid is prepared, and the charge transport layer coating liquid is applied to the surface of the charge generation layer and dried. The film thickness of the charge generation layer thus obtained is not particularly limited, but is preferably 10 to 50 μm, more preferably 15 to 40 μm. Note that a photosensitive layer in which a charge generation material and a charge transport material are present can be formed in one layer. In that case, the type, content, binder resin, and other additives of the charge generation material and the charge transport material may be the same as in the case of separately forming the charge generation layer and the charge transport layer.

  In this embodiment, the photosensitive drum formed by forming the organic photosensitive layer using the charge generation material and the charge transport material as described above is used. Instead, an inorganic photosensitive layer using silicon or the like is formed. Can be used.

  The charging unit 12 faces the photosensitive drum 11 and is arranged so as to be separated from the surface of the photosensitive drum 11 along the longitudinal direction of the photosensitive drum 11 with a gap, and the surface of the photosensitive drum 11 has a predetermined polarity and Charge to potential. As the charging unit 12, a charging brush type charger, a charger type charger, a sawtooth type charger, an ion generator, or the like can be used. In the present embodiment, the charging unit 12 is provided so as to be separated from the surface of the photosensitive drum 11, but is not limited thereto. For example, a charging roller may be used as the charging unit 12 and the charging roller may be disposed so that the charging roller and the photosensitive drum are in pressure contact with each other, or a contact charging type charger such as a charging brush or a magnetic brush may be used. .

  The exposure unit 13 is arranged such that light of each color information emitted from the exposure unit 13 passes between the charging unit 12 and the developing unit 14 and is irradiated on the surface of the photosensitive drum 11. The exposure unit 13 branches the image information into light of each color information of b, c, m, and y in the unit, and the surface of the photosensitive drum 11 charged to a uniform potential by the charging unit 12 is light of each color information. To form an electrostatic latent image on the surface. As the exposure unit 13, for example, a laser scanning unit including a laser irradiation unit and a plurality of reflecting mirrors can be used. In addition, a unit in which an LED array, a liquid crystal shutter, and a light source are appropriately combined may be used.

  The developing unit 14 includes a developing tank 20 and a toner hopper 21. The developing tank 20 is disposed so as to face the surface of the photosensitive drum 11, and is a container that supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum 11 and develops it to form a visible toner image. It is a shaped member. The developing tank 20 accommodates toner in its internal space and accommodates a roller member such as a developing roller, a supply roller, and a stirring roller, or a screw member, and rotatably supports the developing tank 20. An opening is formed in a side surface of the developing tank 20 facing the photosensitive drum 11, and a developing roller is rotatably provided at a position facing the photosensitive drum 11 through the opening. The developing roller is a roller-like member that supplies toner to the electrostatic latent image on the surface of the photoconductor 11 at the pressure contact portion or the closest portion with the photoconductor drum 11. When supplying the toner, a potential having a polarity opposite to the charging potential of the toner is applied to the surface of the developing roller as a developing bias voltage (hereinafter referred to as “developing bias”). As a result, the toner on the surface of the developing roller is smoothly supplied to the electrostatic latent image. Further, by changing the developing bias value, the amount of toner (toner adhesion amount) supplied to the electrostatic latent image can be controlled. The supply roller is a roller-like member provided so as to be able to rotate and face the developing roller, and supplies toner around the developing roller. The agitation roller is a roller-like member that faces the supply roller and can be driven to rotate, and feeds toner newly supplied from the toner hopper 21 into the developing tank 20 to the periphery of the supply roller. The toner hopper 21 is provided so that a toner replenishing port provided at a lower portion in the vertical direction and a toner receiving port provided at an upper portion in the vertical direction of the developing tank 20 communicate with each other. Replenish. Further, the toner hopper 21 may not be used, and the toner may be directly supplied from each color toner cartridge.

  The cleaning unit 15 removes the toner remaining on the surface of the photosensitive drum 11 after transferring the toner image to the recording medium, and cleans the surface of the photosensitive drum 11. For the cleaning unit 15, for example, a plate-like member such as a cleaning blade is used. In the image forming apparatus of the present invention, an organic photosensitive drum is mainly used as the photosensitive drum 11, and the surface of the organic photosensitive drum is mainly composed of a resin component. Deterioration of the surface is likely to proceed due to the chemical action of ozone generated by. However, the deteriorated surface portion is worn by receiving a rubbing action by the cleaning unit 15 and is gradually but surely removed. Therefore, the problem of surface deterioration due to ozone or the like is practically solved, and the charging potential by the charging operation can be stably maintained over a long period of time. Although the cleaning unit 15 is provided in this embodiment, the present invention is not limited to this, and the cleaning unit 15 may not be provided.

  According to the toner image forming unit 2, the surface of the photosensitive drum 11 that is uniformly charged by the charging unit 12 is irradiated with signal light corresponding to the image information from the exposure unit 13 to form an electrostatic latent image. Toner is supplied from the developing means 14 to form a toner image, and after the toner image is transferred to the intermediate transfer belt 25, the toner remaining on the surface of the photosensitive drum 11 is removed by the cleaning unit 15. This series of toner image forming operations is repeatedly executed.

  The transfer unit 3 is disposed above the photosensitive drum 11, and includes an intermediate transfer belt 25, a driving roller 26, a driven roller 27, an intermediate transfer roller 28 (b, c, m, y), and a transfer belt cleaning unit. 29 and the transfer roller 30. The intermediate transfer belt 25 is an endless belt-like member that is stretched by a driving roller 26 and a driven roller 27 to form a loop-shaped movement path, and is driven to rotate in the direction of an arrow S. When the intermediate transfer belt 25 passes through the photosensitive drum 11 while being in contact with the photosensitive drum 11, an intermediate transfer roller 28 disposed on the surface of the photosensitive drum 11 is opposed to the photosensitive drum 11 via the intermediate transfer belt 25. A transfer bias having a polarity opposite to the charging polarity of the toner is applied, and the toner image formed on the surface of the photosensitive drum 11 is transferred onto the intermediate transfer belt 25. In the case of a full-color image, each color toner image formed on each photoconductor drum 11 is sequentially transferred onto the intermediate transfer belt 25 to form a full-color toner image. The driving roller 26 is provided so as to be rotatable around its axis by driving means (not shown), and the intermediate transfer belt 25 is driven to rotate in the arrow S direction by the rotational driving. The driven roller 27 is provided so as to be able to be driven and rotated by the rotational drive of the driving roller 26, and applies a certain tension to the intermediate transfer belt 25 so that the intermediate transfer belt 25 does not loosen. The intermediate transfer roller 28 is provided in pressure contact with the photosensitive drum 11 via the intermediate transfer belt 25 and capable of being driven to rotate about its axis by a driving unit (not shown). The intermediate transfer roller 28 is connected to a power source (not shown) for applying a transfer bias as described above, and has a function of transferring the toner image on the surface of the photosensitive drum 11 to the intermediate transfer belt 25. The transfer belt cleaning unit 29 is provided so as to face the driven roller 27 through the intermediate transfer belt 25 and to contact the outer peripheral surface of the intermediate transfer belt 25. Since the toner adhering to the intermediate transfer belt 25 due to contact with the photosensitive drum 11 causes the back surface of the recording medium to be contaminated, the transfer belt cleaning unit 29 removes and collects the toner on the surface of the intermediate transfer belt 25. The transfer roller 30 is provided in pressure contact with the drive roller 26 via the intermediate transfer belt 25, and can be driven to rotate about an axis by a drive unit (not shown). At the pressure contact portion (transfer nip portion) between the transfer roller 30 and the drive roller 26, the toner image carried and conveyed by the intermediate transfer belt 25 is transferred to the recording medium fed from the recording medium supply means 5 described later. Is done. The recording medium carrying the toner image is fed to the fixing unit 4. According to the transfer unit 3, the toner image transferred from the photosensitive drum 11 to the intermediate transfer belt 25 at the pressure contact portion between the photosensitive drum 11 and the intermediate transfer roller 28 rotates the intermediate transfer belt 25 in the arrow S direction. It is conveyed to a transfer nip portion by driving, and transferred to a recording medium there.

  The fixing unit 4 is provided downstream of the transfer unit 3 in the conveyance direction of the recording medium, and includes a fixing roller 31 and a pressure roller 32. The fixing roller 31 is rotatably provided by a driving unit (not shown), and heats and melts the toner constituting the unfixed toner image carried on the recording medium to fix it on the recording medium. A heating unit (not shown) is provided inside the fixing roller 31. The heating unit heats the fixing roller 31 so that the surface of the fixing roller 31 reaches a predetermined temperature (heating temperature). For example, a heater or a halogen lamp can be used as the heating means. A temperature detection sensor (not shown) is provided near the surface of the fixing roller 31 to detect the surface temperature of the fixing roller 31. The detection result by the temperature detection sensor is written in the storage unit of the control means described later. The pressure roller 32 is provided so as to be in pressure contact with the fixing roller 31 and is supported so as to be driven to rotate by the rotation drive of the pressure roller 32. The pressure roller 32 assists fixing of the toner image on the recording medium by pressing the toner and the recording medium when the toner is melted and fixed on the recording medium by the fixing roller 31. A pressure contact portion between the fixing roller 31 and the pressure roller 32 is a fixing nip portion. According to the fixing unit 4, the recording medium onto which the toner image is transferred by the transfer unit 3 is sandwiched between the fixing roller 31 and the pressure roller 32, and the toner image is recorded under heating when passing through the fixing nip portion. By being pressed against the medium, the toner image is fixed on the recording medium and an image is formed.

  The recording medium supply unit 5 includes an automatic paper feed tray 35, a pickup roller 36, a transport roller 37, a registration roller 38, and a manual paper feed tray 39. If not shown, a surface roughness detection sensor may be included. The automatic paper feed tray 35 is a container-like member that is provided in the lower part of the image forming apparatus 1a in the vertical direction and stores a recording medium. Recording media include plain paper, color copy paper, overhead projector sheets, postcards, and the like. The pick-up roller 36 takes out the recording medium stored in the automatic paper feed tray 35 one by one and feeds it to the paper transport path S1. The conveyance rollers 37 are a pair of roller members provided so as to be in pressure contact with each other, and convey the recording medium toward the registration rollers 38. The registration rollers 38 are a pair of roller members provided so as to be in pressure contact with each other, and the recording medium fed from the conveyance roller 37 is used to convey the toner image carried on the intermediate transfer belt 25 to the transfer nip portion. Synchronously, it is fed to the transfer nip. The manual paper feed tray 39 is a device for taking a recording medium into the image forming apparatus 1a by manual operation, and the recording medium taken from the manual paper feed tray 39 passes through the paper transport path S2 by the transport roller 37. Then, it is fed to the registration roller 38. According to the recording medium supply means 5, the toner image carried on the intermediate transfer belt 25 is conveyed to the transfer nip portion of the recording medium supplied one by one from the automatic paper feed tray 35 or the manual paper feed tray 39. In synchronism with this, the sheet is fed to the transfer nip portion.

  The discharge unit 6 includes a conveyance roller 37, a discharge roller 40, and a discharge tray 41. The conveyance roller 37 is provided downstream of the fixing nip portion in the sheet conveyance direction, and conveys the recording medium on which the image is fixed by the fixing unit 4 toward the discharge roller 40. The discharge roller 40 discharges the recording medium on which the image is fixed to a discharge tray 41 provided on the upper surface in the vertical direction of the image forming apparatus 1a. The discharge tray 41 stores a recording medium on which an image is fixed.

  The image forming apparatus 1a includes a control unit (not shown). The control unit is provided, for example, in an upper part of the internal space of the image forming apparatus 1a, and includes a storage unit, a calculation unit, and a control unit. The storage unit of the control means stores various setting values via an operation panel (not shown) arranged on the upper surface of the image forming apparatus 1a, detection results from sensors (not shown) arranged at various locations inside the image forming apparatus 1a, external devices The image information from is input. In addition, programs for executing various means are written. Examples of the various means include a recording medium determination unit, an adhesion amount control unit, and a fixing condition control unit. As the storage unit, those commonly used in this field can be used, and examples thereof include a read only memory (ROM), a random access memory (RAM), and a hard disk drive (HDD). As the external device, an electrical / electronic device capable of forming or obtaining image information and electrically connected to the image forming apparatus can be used. For example, a computer, a digital camera, a television receiver, a video recorder, Examples include a DVD (Digital Versatile Disc) recorder, an HDDVD (High-Definition Digital Versatile Disc), a Blu-ray disc recorder, a facsimile device, and a portable terminal device. The arithmetic unit takes out various data (image formation command, detection result, image information, etc.) written in the storage unit and programs of various means, and performs various determinations. The control unit sends a control signal to the corresponding device according to the determination result of the calculation unit, and performs operation control. The control unit and the calculation unit include a processing circuit realized by a microcomputer, a microprocessor, or the like provided with a central processing unit (CPU). The control means includes a main power supply together with the processing circuit described above, and the power supply supplies power not only to the control means but also to each device in the image forming apparatus 1a.

  According to the image forming apparatus 1a, after the toner image formed by the toner image forming unit 2 is transferred to the intermediate transfer belt 25 of the transfer unit 3, the toner image on the intermediate transfer belt 25 is transferred to a recording medium. The toner image on the recording medium and the recording medium are discharged by the discharging means A, the toner image is fixed on the recording medium by the fixing means 4 to form an image, and the image-formed recording medium is discharged by the discharging roller 40 of the discharging means 6. Via, it is discharged to the discharge tray 41.

  FIG. 2 is a cross-sectional view schematically showing a configuration of an image forming apparatus 1b according to the second embodiment of the present invention. The image forming apparatus 1b is obtained by further adding a charging unit B to the image forming apparatus 1a.

  Here, the charging means B of the present invention will be described. The charging unit B is on the downstream side of the toner image forming unit 2 with respect to the rotational driving direction S of the intermediate transfer belt 25, on the upstream side of the transfer unit 3, and on the surface of the intermediate transfer belt 25 on which the toner image is formed. The toner is disposed so as to be separated from the intermediate transfer belt 25 and charges the toner to a predetermined polarity and potential. As the charging means B, a charger-type charger, a saw-tooth type charger, an ion generator, or the like can be used, but is not particularly limited thereto.

  Since the charging unit B is provided upstream of the transfer unit 3 with respect to the rotational driving direction S of the intermediate transfer belt 25 and the toner charge amount of the toner image is increased before the transfer, the transferability at the time of transfer is improved. , Dot missing is eliminated and dot reproducibility is improved.

  The charging amount of the toner is increased by the charging unit B, but the neutralization unit A is provided between the transfer unit 3 and the fixing unit 4 to sufficiently neutralize the toner, so that the toner and the fixing roller in the fixing nip portion The electric repulsive force between the two can be reduced, and the occurrence of toner scattering can be prevented. As a result, an image without toner scattering can be formed.

  The absolute value of the toner charge amount of the charged toner image is preferably 20 μC / g or more and 40 μC / g or less. This improves transferability and reduces missing dots.

  When the absolute value of the toner charge amount is less than 20 μC / g, the transferability of the toner is lowered and dot missing occurs. When the absolute value of the toner charge amount exceeds 40 μC / g, the electrostatic adhesion force between the intermediate transfer belt and the toner becomes strong, and the transferability is deteriorated.

  Here, the toner charge amount is obtained by sucking the toner on the intermediate transfer belt 25 after passing through the charging means B using a charge amount measuring device (trade name: 210HS-2A, manufactured by Trek Japan Co., Ltd.). The toner charge amount Q / M (μC / g) can be obtained by dividing the charge amount Q (μC) of the toner by the suction toner weight M (g).

  Here, the toner is not particularly limited, and a toner containing a binder resin, a colorant, a release agent, a charge control agent, an external additive, and the like can be used. The binder resin is not particularly limited as long as it is commonly used as a binder resin for toner and can be granulated in a molten state, and known resins can be used, for example, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, Polyester, polyamide, styrene polymer, (meth) acrylic resin, polyvinyl butyral, silicone resin, polyurethane, epoxy resin, epoxy resin, phenol resin, xylene resin, rosin modified resin, terpene resin, aliphatic hydrocarbon resin, alicyclic Examples include hydrocarbon resins, aromatic petroleum resins, chlorinated paraffins, and paraffin waxes. Binder resin can be used individually by 1 type, or can use 2 or more types together. Among these, polyester, styrene polymer, (meth) acrylic resin, and the like whose particle surface is easily smoothed by wet granulation in water are preferable.

  As the polyester, a polycondensate of a polyhydric alcohol and a polycarboxylic acid is preferable. Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, diethylene glycol, 1,5-pentanediol, and 1,6-hexanediol. And aliphatic alcohols such as neopentyl glycol, alicyclic alcohols such as cyclohexanedimethanol and hydrogenated bisphenol, and bisphenol A alkylene oxide adducts such as bisphenol A ethylene oxide adduct and bisphenol A propylene oxide adduct. The polyhydric alcohol can use 1 type (s) or 2 or more types. Examples of polyvalent carboxylic acids include saturated and unsaturated aromatic carboxylic acids such as phthalic acid, terephthalic acid, and phthalic anhydride and their anhydrides, succinic acid, adipic acid, sebacic acid, azelaic acid, and dodecenyl succinic acid. Examples thereof include aliphatic carboxylic acids and acid anhydrides thereof. One or more polycarboxylic acids can be used.

  Examples of the styrenic polymer include homopolymers of styrenic monomers and copolymers of styrene monomers and monomers copolymerizable with styrenic monomers. Examples of the styrene monomer include styrene, o-methyl styrene, ethyl styrene, p-methoxy styrene, p-phenyl styrene, 2,4-dimethyl styrene, pn-octyl styrene, pn-decyl styrene, p. -N-dodecyl styrene etc. are mentioned. Other monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, (meth) acrylate n- (Meth) acrylates such as octyl, dodecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, stearyl (meth) acrylate, phenyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, (Meth) acrylic monomers such as acrylonitrile, methacrylamide, glycidyl methacrylate, N-methylol acrylamide, N-methylol methacrylamide, 2-hydroxyethyl acrylate, vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether Vinyl ethers, vinyl methyl ketone, vinyl hexyl ketone, vinyl ketones such as methyl isopropenyl ketone, N- vinylpyrrolidone, N- vinyl carbazole, etc. N- vinyl compounds such as N- vinyl indole, and the like. The styrene monomer and the monomer copolymerizable with the styrene monomer can be used alone or in combination of two or more.

  Examples of the (meth) acrylic resin include homopolymers of (meth) acrylic acid esters, copolymers of (meth) acrylic acid esters and monomers copolymerizable with (meth) acrylic acid esters, and the like. As the (meth) acrylic acid esters, the same ones as described above can be used. Examples of the monomer copolymerizable with (meth) acrylic acid esters include (meth) acrylic monomers, vinyl ethers, vinyl ketones, and N-vinyl compounds. These can be the same as those described above.

  It is also possible to use a binder resin in which a hydrophilic group such as a carboxyl group or a sulfonic acid group is bonded to the main chain or side chain of the binder resin to impart self-dispersibility in water.

  Examples of the colorant that can be used include black pigments and chromatic pigments. Examples of black pigments include black inorganic pigments such as carbon black, copper oxide, manganese dioxide, activated carbon, nonmagnetic ferrite, magnetic ferrite, and magnetite, and black organic pigments such as aniline black. Examples of chromatic pigments include yellow inorganic pigments such as yellow lead, zinc lead, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa Yellow G, Hansa Yellow 10G. , Benzidine yellow G, benzidine yellow GR, yellow organic pigments such as quinoline yellow lake, permanent yellow NCG, tartrazine lake, orange inorganic pigments such as red yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, Orange organic pigments such as Induslen Brilliant Orange RK, Benzidine Orange G, Induslen Brilliant Orange GK, Reds such as Bengala, Cadmium Red, Lead Red, Mercury Sulfide, Cadmium Red pigments such as machine pigments, permanent red 4R, resol red, pyrazolone red, watching red, calcium salt, lake red C, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B , Purple inorganic pigments such as manganese purple, purple organic pigments such as fast violet B and methyl violet lake, blue inorganic pigments such as bitumen and cobalt blue, alkali blue lake, victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue , Phthalocyanine blue partially chlorinated products, blue organic pigments such as first sky blue and indanthrene blue BC, green inorganic pigments such as chrome green and chromium oxide, pigment green B, mica light green lake, such as the green-based organic pigments, such as final yellow green G and the like. One or more colorants can be used. Two or more colorants of the same color may be used, or different colors may be mixed and used. The content of the colorant is preferably 1 to 20% by weight of the total amount of toner particles, and more preferably 0.2 to 10% by weight of the total amount of toner particles.

  As the release agent, those commonly used in this field can be used, for example, petroleum wax such as paraffin wax and derivatives thereof, microcrystalline wax and derivatives thereof, Fischer-Tropsch wax and derivatives thereof, polyolefin wax and derivatives thereof, Molecular weight polypropylin wax and its derivatives, polyolefin polymer wax (low molecular weight polyethylene wax and the like) and its hydrocarbon synthetic waxes, carnauba wax and its derivatives, rice wax and its derivatives, candelilla wax and its derivatives, Plant waxes such as wood wax, animal waxes such as beeswax and spermaceti, fats and oils synthetic waxes such as fatty acid amides and phenol fatty acid esters, long chain carboxylic acids and their derivatives, long chain alcohols and their derivatives, silicone Polymer, such as a higher fatty acid, and the like. Derivatives include oxides, block copolymers of vinyl monomers and waxes, graft modified products of vinyl monomers and waxes, and the like. The amount of wax used is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.2 to 20% by weight based on the total amount of toner particles.

  Examples of the charge control agent include metal-containing azo dyes (chromium / azo complex dyes, iron azo complex dyes, cobalt / azo complex dyes, etc.), copper phthalocyanine dyes, metals of salicylic acid and alkyl derivatives thereof (chromium, zinc, aluminum, Boron) complexes and salts thereof, naphtholic acid and its derivatives metal (chromium, zinc, aluminum, boron etc.) complexes and salts, benzylic acid and its derivatives (chrome, zinc, aluminum, boron etc.) complexes and their Salt, long-chain alkyl carboxylate, long-chain alkyl sulfonate and other negative charge toner charge control agent, nigrosine dye and its derivatives, benzoguanamine, triphenylmethane derivative, quaternary ammonium salt, quaternary phosphonium salt, 4 Grade Pyridinium salt, Guanidine salt, Amidine salt, Nitrogen-containing functional group Monomers [N, N-dialkylaminoalkyl (meth) acrylates such as N, N-dimethylaminomethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, etc. , N, N-dimethylaminoethyl (meth) acrylamide, and N, N-dialkylaminoalkyl (meth) acrylamides such as N, N-dimethylaminopropyl (meth) acrylamide]. It is done. One or more charge control agents can be used. The content of the charge control agent is preferably 0.1 to 5.0% by weight based on the total amount of toner particles.

  The toner can be produced by, for example, a melt-kneading pulverization method. According to the melt-kneading pulverization method, a predetermined amount of each of a binder resin, a colorant, a release agent, a charge control agent, and other additives is dry-mixed, the resulting mixture is melt-kneaded, and the resulting melt-kneaded product Can be cooled and solidified, and the resulting solidified product can be mechanically pulverized. As a mixer used for dry mixing, for example, Henschel mixer (trade name, manufactured by Mitsui Mining Co., Ltd.), super mixer (trade name, manufactured by Kawata Co., Ltd.), mechano mill (trade name, manufactured by Okada Seiko Co., Ltd.), etc. Examples include a Henschel type mixing device, Ongmill (trade name, manufactured by Hosokawa Micron Corporation), hybridization system (trade name, manufactured by Nara Machinery Co., Ltd.), and Cosmo system (trade name, manufactured by Kawasaki Heavy Industries, Ltd.). The kneading is performed while stirring and heating to a temperature equal to or higher than the melting temperature of the binder resin (usually about 80 to 200 ° C., preferably about 100 to 150 ° C.). As a kneading machine, for example, a general kneading machine such as a twin screw extruder, a triple roll, a lab blast mill can be used. More specifically, for example, a uniaxial or biaxial extruder such as TEM-100B (trade name, manufactured by Toshiba Machine Co., Ltd.), PCM-65 / 87 (trade name, manufactured by Ikegai Co., Ltd.), Needex ( Open roll type products such as trade name, manufactured by Mitsui Mining Co., Ltd.). Among these, an open roll type is preferable. Examples of the pulverization of the solidified product obtained by cooling the melt-kneaded product include a cutter mill, a feather mill, and a jet mill. For example, the solidified product is roughly pulverized with a cutter mill and then pulverized with a jet mill, whereby a toner having a desired volume average particle diameter is obtained.

  At least a part of the toner particles produced as described above may be spheroidized, and examples of the means for spheronizing include an impact spheronizing device and a hot air spheronizing device. As the impact spheroidizing device, a commercially available device can be used. For example, a faculty (trade name, manufactured by Hosokawa Micron Corporation), a hybridization system (trade name, manufactured by Nara Machinery Co., Ltd.), or the like is used. be able to. Or as a hot-air type | formula spheronization apparatus, what is marketed can also be used, for example, surface modification machine meteo olebo (brand name, Nippon Pneumatic Industry Co., Ltd. product) etc. can be used.

  Among the toners thus obtained, the circularity of the toner used in the image forming apparatuses 1a and 1b of the present invention is preferably in the range of 0.955 to 0.975. This improves transferability and eliminates missing dots, thereby improving dot reproducibility.

  When the circularity is less than 0.955, transferability is reduced and dot missing occurs, so that a good image cannot be formed. If the circularity exceeds 0.975, the non-electrostatic adhesion force becomes weak. Therefore, even if the charge amount of the toner on the recording medium is reduced by using the charge eliminating means, the electric interaction with the fixing roller is small. Toner scattering occurs. Also, a cleaning failure occurs in the cleaning unit.

Here, the circularity (ai) of the toner particles is defined by the following formula (3). The circularity (ai) as defined in Formula (3) is measured by using, for example, a flow type particle image analyzer (trade name: FPIA-3000, manufactured by Sysmex Corporation). Further, the sum of the respective circularities (ai) measured for m toner particles is obtained, and the arithmetic average value obtained by Expression (4) obtained by dividing the sum by the number of toner particles m is defined as the average circularity (a).
Circularity (ai) = (perimeter of a circle having the same projected area as the particle image)
/ (Peripheral length of projected image of particle) (3)

  In the flow-type particle image analyzer, after calculating the circularity (ai) of each toner particle, the circularity (ai) of each toner particle obtained is calculated every 0.01 from 0.01 to 1.00. A simple calculation method is used in which the frequency is obtained by dividing each of the divided ranges into 61 and the average circularity is calculated using the center value and the frequency of each divided range. The error between the average circularity value calculated by this simple calculation method and the average circularity (a) value given by the equation (4) is very small and can be substantially ignored. In the embodiment, the average circularity by the simple calculation method is handled as the average circularity (a) defined by the above formula (4).

  A specific method for measuring the average circularity (a) is as follows. A dispersion is prepared by dispersing 5 mg of toner in 10 mL of water in which about 0.1 mg of a surfactant is dissolved, and the dispersion is irradiated with ultrasonic waves having a frequency of 20 kHz and an output of 50 W for 5 minutes. The circularity (ai) was measured with a flow-type particle image analyzer at a particle concentration of 5000 to 20000 particles / μL, and the average circularity (a) was determined.

  The volume average particle diameter of the toner is preferably in the range of 4 μm to 8 μm. This improves dot reproducibility. Further, it is possible to form a high-quality image with good fine line reproducibility.

  When the volume average particle size is less than 4 μm, the non-electrostatic adhesion force of the toner is increased, so that the transferability is deteriorated and dot missing occurs. On the other hand, if the volume average particle size exceeds 8 μm, dot reproducibility and fine line reproducibility deteriorate, and a high-quality image cannot be formed.

  Here, the volume average particle diameter is a value obtained as follows. To 50 ml of an electrolyte (trade name: ISOTON-II, manufactured by Beckman Coulter, Inc.), 20 mg of a sample and 1 ml of alkyl ether sulfate sodium are added, and an ultrasonic disperser (trade name: UH-50, manufactured by SMT Co., Ltd.) is used. A sample for measurement is prepared by dispersing for 3 minutes at an ultrasonic frequency of 20 kHz. About this measurement sample, using a particle size distribution measuring device (trade name: Multisizer 2, manufactured by Beckman Coulter, Inc.), measurement is performed under the conditions of an aperture diameter of 100 μm and the number of measured particles of 50000 counts. The volume average particle diameter can be calculated.

  Further, the toner particles produced as described above have functions such as powder flowability improvement, triboelectric chargeability improvement, heat resistance, long-term storability improvement, cleaning property improvement and photoreceptor surface wear property control. An external additive may be mixed. Examples of the external additive include silica fine powder, titanium oxide fine powder, and alumina fine powder. One type of external additive can be used alone, or two or more types can be used in combination. The external additive is added in an amount of 0.1 to 100 parts by weight of the toner particles in consideration of the charge amount necessary for the toner, the effect of adding the external additive on the wear of the photoreceptor and the environmental characteristics of the toner. 1 to 10 parts by weight is preferred.

  In the present invention, it is preferable to add 0.2 to 3 parts by weight of titanium oxide as an external additive with respect to 100 parts by weight of the toner. As a result, the toner resistance can be controlled, and transfer of charges generated by the charging means or the charge eliminating means can be made smooth so that the desired charge amount can be easily adjusted.

  When the addition amount of titanium oxide is less than 0.2 parts by weight, it becomes difficult to control the toner resistance, and thus it is difficult to adjust to a desired charge amount. When the addition amount of titanium oxide exceeds 3 parts by weight, the charging ability of the toner is lowered, and even when a charging unit is used, the amount of charge does not increase and the transferability is lowered, resulting in dot missing. Further, since the charge amount is too small in the static elimination means, the electrostatic adhesion to the recording medium is weakened, so that the toner image is disturbed and the inside of the apparatus may be contaminated.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not particularly limited as long as it does not exceed the gist thereof. In the following, “parts” and “%” mean “parts by weight” and “% by weight” unless otherwise specified. In Examples and Comparative Examples, the glass transition point (Tg) of the binder resin, the volume average particle diameter and the average circularity of the toner were measured as follows.

[Glass transition point of binder resin (Tg)]
Using a differential scanning calorimeter (trade name: DSC220, manufactured by Seiko Denshi Kogyo Co., Ltd.), according to Japanese Industrial Standard (JIS) K7121-1987, 1 g of a sample was heated at a heating rate of 10 ° C. per minute and a DSC curve was measured. did. Draw the endothermic peak corresponding to the glass transition of the obtained DSC curve at a point where the slope is maximum with respect to the straight line that extends the base line on the high temperature side to the low temperature side and the curve from the rising part of the peak to the vertex. The temperature at the intersection with the tangent was determined as the glass transition point (Tg).

[Volume average particle diameter of toner]
To 50 ml of electrolyte (trade name: ISOTON-II, manufactured by Beckman Coulter, Inc.), 20 mg of sample and 1 ml of sodium alkyl ether sulfate are added, and an ultrasonic disperser (trade name: UH-50, manufactured by SMT Co., Ltd.) is used. A sample for measurement was prepared by a dispersion treatment at an ultrasonic frequency of 20 kHz for 3 minutes. About this measurement sample, using a particle size distribution measuring apparatus (trade name: Multisizer 3, manufactured by Beckman Coulter, Inc.), measurement is performed under the conditions of an aperture diameter of 100 μm and the number of measured particles of 50000 counts. The volume average particle size was determined.

[Average circularity of toner]
A dispersion is prepared by dispersing 5 mg of toner in 10 mL of water in which about 0.1 mg of a surfactant is dissolved, and the dispersion is irradiated with ultrasonic waves having a frequency of 20 kHz and an output of 50 W for 5 minutes. The circularity (ai) was measured with the above-mentioned flow type particle image analyzer (trade name: FPIA-3000, manufactured by Sysmex Corporation) at a particle concentration of 5000 to 20000 particles / μL. Moreover, average circularity (a) was computed from the measurement result of this circularity by said Formula (4).

(Production of first toner)
100 parts of polyester (binder resin, trade name: Toughton, manufactured by Kao Corporation, glass transition point 70 ° C.), C.I. I. Pigment Blue 15: 3 (colorant, manufactured by Dainichi Seika Kogyo Co., Ltd.) 6.1 parts and organoboron compound (charge control agent, trade name: LR-147, manufactured by Nippon Carlit Co., Ltd.) 1.2 parts The toner raw material 45 kg contained in a ratio (part) was mixed for 7 minutes by a Henschel mixer (trade name: FM mixer, manufactured by Mitsui Mining Co., Ltd.). This raw material mixture was melt-kneaded with a twin-screw extrusion kneader (trade name: PCM65, manufactured by Ikegai Co., Ltd.), cooled to room temperature, and then the solidified product of the melt-kneaded product was cut into a cutting mill (trade name: VM-16, Rishi After coarsely pulverizing with a counter jet mill, the excessively pulverized toner was classified and removed with a rotary classifier to obtain a pulverized resin composition having a volume average particle size of 6 μm.

  Subsequently, the pulverized product of the resin composition after classification was spheroidized by a hot air spheronizing device (trade name: Meteole Inbo, manufactured by Nippon Pneumatic Industry Co., Ltd.). In the hot air spheronizer, the temperature of the hot air was 180 ° C.

  To 100 parts of the spheroidized resin composition thus obtained, as external additives, 1.0 part of titanium oxide having an average primary particle diameter of 30 nm and silica fine particles having an average primary particle diameter of 20 nm. 0 part was added and mixed for 3 minutes using a Henschel mixer (trade name: FM20C, manufactured by Mitsui Mining Co., Ltd.) at a peripheral speed of 35 m / s to obtain a negatively charged first toner. The volume average particle diameter of the first toner was 6 μm, and the average circularity was 0.960.

(Production of second toner)
In the hot air spheronizer, the second toner was obtained by the same method as the first toner except that the temperature of the hot air was 150 ° C. The volume average particle diameter of the second toner was 6 μm, and the average circularity was 0.955.

(Production of third toner)
In the hot air spheronizer, the third toner was obtained in the same manner as the first toner except that the temperature of the hot air was 220 ° C. The volume average particle diameter of the third toner was 6 μm, and the average circularity was 0.975.

(Fabrication of fourth toner)
A fourth toner was obtained in the same manner as the first toner, except that the pulverized product of the resin composition having a volume average particle size of 4 μm was obtained by changing the operating conditions during classification. The volume average particle size of the fourth toner was 4 μm, and the average circularity was 0.961.

(Production of fifth toner)
A fifth toner was obtained in the same manner as the first toner, except that the pulverized product of the resin composition having a volume average particle size of 8 μm was obtained by changing the operating conditions during classification. The volume average particle diameter of the fifth toner was 8 μm, and the average circularity was 0.958.

(Production of sixth toner)
A sixth toner was obtained in the same manner as the first toner except that the amount of titanium oxide added was 0.2 parts. The volume average particle size of the sixth toner was 6 μm, and the average circularity was 0.960.

(Production of seventh toner)
A seventh toner was obtained in the same manner as the first toner except that the amount of titanium oxide added was 3.0 parts. The seventh toner had a volume average particle size of 6 μm and an average circularity of 0.960.

(Production of eighth toner)
In the hot air spheronizer, an eighth toner was obtained by the same method as the first toner except that the temperature of the hot air was 120 ° C. The eighth toner had a volume average particle size of 6 μm and an average circularity of 0.950.

(Production of ninth toner)
In the hot air spheronizer, a ninth toner was obtained in the same manner as the first toner except that the temperature of the hot air was 230 ° C. The ninth toner had a volume average particle size of 6 μm and an average circularity of 0.980.

(Production of tenth toner)
A tenth toner was obtained in the same manner as the first toner, except that the operating conditions during classification were changed to obtain a pulverized resin composition having a volume average particle size of 3.5 μm. The tenth toner had a volume average particle size of 3.5 μm and an average circularity of 0.963.

(Production of 11th toner)
An eleventh toner was obtained in the same manner as the first toner, except that the pulverized product of the resin composition having a volume average particle size of 8.5 μm was obtained by changing the operating conditions for classification. The eleventh toner had a volume average particle size of 8.5 μm and an average circularity of 0.955.

(Production of 12th toner)
A twelfth toner was obtained in the same manner as the first toner except that the amount of titanium oxide added was 0.1 part. The twelfth toner had a volume average particle size of 6 μm and an average circularity of 0.960.

(Production of 13th toner)
A thirteenth toner was obtained in the same manner as the first toner except that the amount of titanium oxide added was 3.5 parts. The thirteenth toner had a volume average particle size of 6 μm and an average circularity of 0.960.

(Preparation of two-component developer)
5 parts of each of the first to thirteenth toners and 95 parts of a ferrite core carrier having a volume average particle size of 45 μm as a carrier are placed in a V-type mixer / mixer (trade name: V-5, manufactured by Tokuju Kakujo Co., Ltd.) For 20 minutes to obtain first to thirteenth two-component developers having a toner concentration of 5%.

Example 1
The image forming apparatus 1a was used, and a wire-type static eliminator having a discharge start voltage Vs of 2 kV was used as the static eliminator A. The superimposed voltage Vdc applied to the static elimination means A was 1.5 kV, and the applied AC voltage had an amplitude Vp of 5 kV and a frequency of 800 Hz. At this time, the first two-component developer was used. The sum of | Vdc | and | Vs | is 3.5 kV, which is smaller than Vp, and therefore satisfies Expression (1).

(Example 2)
The same setting as in Example 1 was performed except that the superposed voltage Vdc applied to the static eliminating means A was set to 1 kV. The sum of | Vdc | and | Vs | is 3 kV, which is smaller than Vp, and therefore satisfies Expression (1).

(Example 3)
The setting was made in the same manner as in Example 1 except that the superposed voltage Vdc applied to the static elimination means A was 2 kV. The sum of | Vdc | and | Vs | is 4 kV, which is smaller than Vp, and therefore satisfies Expression (1).

Example 4
The image forming apparatus 1b was used, and a wire-type static eliminator having a discharge start voltage Vs of 2 kV was used as the static eliminator A. The superimposed voltage Vdc applied to the static elimination means A was 1.5 kV, and the applied AC voltage had an amplitude Vp of 5 kV and a frequency of 800 Hz. The DC voltage Ve applied to the charging means B was 4 kV. At this time, the first two-component developer was used. The sum of | Vdc | and | Vs | is 3.5 kV, which is smaller than Vp, and therefore satisfies Expression (1).

(Example 5)
The setting was made in the same manner as in Example 4 except that the DC voltage Ve applied to the charging means B was 3.5 kV.

(Example 6)
Setting was performed in the same manner as in Example 4 except that the DC voltage Ve applied to the charging means B was 4.5 kV.

(Example 7)
Settings were made in the same manner as in Example 4 except that the second two-component developer was used.

(Example 8)
Settings were made in the same manner as in Example 4 except that the third two-component developer was used.

Example 9
Settings were made in the same manner as in Example 4 except that the fourth two-component developer was used.

(Example 10)
Settings were made in the same manner as in Example 4 except that the fifth two-component developer was used.

Example 11
Settings were made in the same manner as in Example 4 except that the sixth two-component developer was used.

Example 12
Settings were made in the same manner as in Example 4 except that the seventh two-component developer was used.

(Example 13)
The setting was made in the same manner as in Example 1 except that the superimposed voltage Vdc applied to the static elimination means A was set to 0.5 kV. The sum of | Vdc | and | Vs | is 2.5 kV, which is smaller than Vp, and therefore satisfies Expression (1).

(Example 14)
The setting was made in the same manner as in Example 1 except that the superposed voltage Vdc applied to the static elimination means A was 2.5 kV. The sum of | Vdc | and | Vs | is 4.5 kV, which is smaller than Vp, and therefore satisfies Expression (1).

(Example 15)
The same setting as in Example 4 was performed except that the DC voltage Ve applied to the charging means B was 3 kV.

(Example 16)
Setting was performed in the same manner as in Example 4 except that the DC voltage Ve applied to the charging means B was 5.5 kV.

(Example 17)
Settings were made in the same manner as in Example 4 except that the eighth two-component developer was used.

(Example 18)
Settings were made in the same manner as in Example 4 except that the ninth two-component developer was used.

Example 19
The same setting as in Example 4 was performed except that the tenth two-component developer was used.

(Example 20)
Settings were made in the same manner as in Example 4 except that the eleventh two-component developer was used.

(Example 21)
Settings were made in the same manner as in Example 4 except that the twelfth two-component developer was used.

(Example 22)
Settings were made in the same manner as in Example 4 except that the 13th two-component developer was used.

(Comparative Example 1)
Settings were made in the same manner as in Example 1 except that the superimposed voltage Vdc was not applied to the charge removal means A.

(Comparative Example 2)
The setting was made in the same manner as in Example 1 except that the superposed voltage Vdc applied to the static elimination means A was 3 kV. The sum of | Vdc | and | Vs | is 5 kV, which is equal to Vp, and therefore does not satisfy Expression (1).

(Comparative Example 3)
The setting was made in the same manner as in Example 1 except that the superposed voltage Vdc applied to the static eliminating means A was 4 kV. The sum of | Vdc | and | Vs | is 6 kV, which is larger than Vp, and therefore does not satisfy Expression (1).

  Table 1 shows the image forming apparatus and toner (volume average particle diameter, average circularity, added amount of titanium oxide) and voltage values used in Examples and Comparative Examples.

  An image was formed by the following method under the conditions of the example and the comparative example, and the toner charge amount was measured.

[Toner charge amount]
The image forming apparatus of the present invention was filled with a two-component developer containing toner and adjusted so that the toner adhesion amount on the photoreceptor was 0.4 mg / cm ² to form a solid image with a printing rate of 100%. .

The toner charge amount is determined by charging the toner on the recording medium after passing through the charge removal means A and the toner on the intermediate transfer belt 25 after passing through the charge means B, respectively. The toner charge amount Q / M (μC / g) was obtained by dividing the charge amount Q (μC) at that time by the suction toner weight M (g).
Table 1 shows the toner charge amount after charge removal and after charge.

Images were formed and evaluated by the following methods under the conditions of Examples and Comparative Examples.
[Dot scattering]
The two-component developer containing toner is filled in the image forming apparatus of the present invention, and the toner adhesion amount on the photoreceptor is adjusted to 0.4 mg / cm ² to form an image of 3 × 5 isolated dots. . An image of 3 × 5 isolated dots is such that, at 600 dpi (dot per inch), a plurality of dot portions each having a size of 3 vertical dots and 3 horizontal dots have an interval between adjacent dot portions of 5 dots. This is an image to be formed. The formed image was magnified 200 times with an optical microscope (trade name: VHX-600, manufactured by Keyence Corporation), and scattering around dots (3 × 3) was visually counted and judged. The evaluation criteria are as follows.
A: Very good. Toner scattering is less than 20.
○: Good. Toner scattering is 20 or more and less than 30.
Δ: Actual use is possible. Toner scattering is 30 or more and less than 50.
×: Unusable. Toner scattering is 50 or more.

[Dot missing]
The two-component developer containing toner is filled in the image forming apparatus of the present invention, and the toner adhesion amount on the photoreceptor is adjusted to 0.4 mg / cm ² to form an image of 3 × 5 isolated dots. . An image of 3 × 5 isolated dots is such that, at 600 dpi (dot per inch), a plurality of dot portions each having a size of 3 vertical dots and 3 horizontal dots have an interval between adjacent dot portions of 5 dots. This is an image to be formed. The formed image is magnified 100 times with an optical microscope (trade name: VHX-600, manufactured by Keyence Corporation) and displayed on the monitor, and the number of missing dots among 70 3 × 5 isolated dots is confirmed. did. The evaluation criteria are as follows.
A: Very good. There are less than 4 missing dots.
○: Good. There are 4 to less than 7 missing dots.
Δ: Actual use is possible. There are 7 or more and less than 11 missing dots.
×: Unusable. There are 11 or more missing dots.

[Resolution]
Conditions under which an image forming apparatus of the present invention is filled with a two-component developer containing toner and an image density is 0.3 and a halftone image having a diameter of 5 mm can be copied at an image density of 0.3 to 0.5. The original on which a fine line original image having a line width of 100 μm was formed was copied, and the obtained copy image was used as a measurement sample. The line width of the thin line formed on the measurement sample by the indicator was measured from a monitor image obtained by enlarging the measurement sample 100 times using a particle analyzer (trade name: Luzex 450, manufactured by Nireco Corporation). The image density is an optical reflection density measured by a reflection densitometer (trade name: RD-918, manufactured by Macbeth). Since the thin line has irregularities and the line width varies depending on the measurement position, the line width is measured at a plurality of measurement positions and an average value is obtained, and this line width is taken as the line width of the measurement sample. The line width of the measurement sample was divided by the original line width of 100 μm, and the obtained value was multiplied by 100 to obtain a fine line reproducibility value. The closer the value of the fine line reproducibility is to 100, the better the fine line reproducibility and the better the resolution. The evaluation criteria are as follows.
A: Fine line reproducibility is 100 or more and less than 105.
○: Fine line reproducibility is 105 or more and less than 115.
(Triangle | delta): The value of fine line reproducibility is 115-125.
X: Fine line reproducibility value of 125 or more.

[Removability of recording medium (jam)]
The image forming apparatus of the present invention was filled with a two-component developer containing toner and adjusted so that the toner adhesion amount on the photoreceptor was 0.4 mg / cm ² to form a solid image with a printing rate of 100%. .

In Examples and Comparative Examples, it was confirmed whether or not jamming occurred due to defective peeling of the recording medium from the conveying member. The evaluation criteria are as follows.
○: Good. Peeling is done smoothly without jamming.
X: Defect. A jam occurs.

〔Comprehensive evaluation〕
A total evaluation was performed based on the following criteria, combining the results of dot scattering, dot omission, peelability of the recording medium, and resolution.
A: Very good. There are no x and Δ, and there are 3 or more.
○: Good. There is no x and Δ.
Δ: Actual use is possible. There is no x and there is a triangle.
X: Defect. There are one or more x's.

  Table 2 shows the evaluation results and overall evaluation results of dot scattering, dot dropout, resolution, and peelability (jam) of the recording medium.

  In Examples 1 to 12, there was no toner scattering or dot missing, and images with excellent resolution and good dot reproducibility were obtained.

  On the other hand, Comparative Example 1 does not apply the superimposed voltage, and thus the paper peelability is good, but the toner scatters at the fixing nip.

  In Comparative Examples 2 and 3, the formula (1) was not satisfied, and the paper peelability was poor and jamming occurred.

  In Example 13, Vdc is small and the above formula (2) is not satisfied, and in Example 21, the amount of charge after static elimination is small because of the small amount of titanium oxide added. Due to the large number of dots, some dot scattering occurred, but there was no problem in actual use.

  In Example 14, Vdc is large and the above formula (2) is not satisfied, and in Example 22, the amount of charge after static elimination is − Although the resolution was slightly lower because the image was less than 10 μC / g and the image was disturbed during conveyance of the recording medium, there was no problem in practical use.

  In Examples 15 and 16, since the charge amount before transfer was not optimal, transferability was slightly deteriorated and dots were slightly removed, but there was no problem in actual use.

  Further, in Examples 17 and 19, since the non-electrostatic adhesive force was strong and the transferability was slightly deteriorated, the dots were slightly removed, but there was no problem in practical use.

  In Example 18, since the non-electrostatic adhesion to the recording medium was weak, a little dot scattering occurred, but there was no problem in practical use.

  In Example 20, since the toner particle size was as large as 8.5 μm, the resolution was slightly deteriorated and the dot reproducibility was slightly deteriorated, but there was no problem in practical use.

It is sectional drawing which shows typically the structure of the image forming apparatus 1a which is 1st Embodiment of this invention. It is sectional drawing which shows typically the structure of the image forming apparatus 1b which is the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Image forming apparatus 2 Toner image forming means 3 Transfer means 4 Fixing means 5 Recording medium supply means 6 Ejecting means 11 Photosensitive drum 12 Charging means 13 Exposure unit 14 Developing means 15 Cleaning unit 20 Developing tank 21 Toner hopper 25 Intermediate transfer belt 26 driving roller 27 driven roller 28 intermediate transfer roller 29 transfer belt cleaning unit 30 transfer roller 31 fixing roller 32 pressure roller 35 automatic paper feed tray 36 pickup roller 37 transport roller 38 registration roller 39 manual paper feed tray 40 discharge roller 41 discharge Tray A Static elimination means B Charging means

Claims (8)

An image carrier that carries and conveys a toner image formed according to image information;
Transfer means for electrostatically transferring the toner image carried on the image carrier to a recording medium;
Neutralizing means for neutralizing the toner image transferred to the recording medium and the recording medium;
Fixing means for fixing the discharged toner image to the discharged recording medium,
The static elimination means includes
Provided on the downstream side of the transfer unit and the upstream side of the fixing unit in the conveyance direction of the recording medium;
The recording medium is disposed so as to face the side through which the toner image is transferred.
Apply a voltage superimposed on the opposite polarity side of the toner image,
An image forming apparatus characterized in that when the amplitude of the AC voltage is Vp, the superimposed voltage is Vdc, and the discharge start voltage is Vs, the following equation (1) is satisfied.
Vp> | Vdc | + | Vs | (1) The static elimination means includes
Apply a voltage superimposed on the opposite polarity side of the toner image,
2. The image forming apparatus according to claim 1, wherein when the amplitude of the AC voltage is Vp, the superimposed voltage is Vdc, and the discharge start voltage is Vs, the following expression (2) is satisfied.
0.5 <Vp− (| Vdc | + | Vs |) <2.5 (2)   The image forming apparatus according to claim 1, wherein an absolute value of a toner charge amount of the discharged toner image is 10 μC / g or more and 25 μC / g or less. The transfer means includes
An intermediate transfer body that receives an intermediate transfer of a toner image carried on the image carrier at an intermediate transfer position and moves the toner image to a transfer position by moving in a predetermined direction while carrying the toner image;
The image forming apparatus according to claim 1, further comprising a charging unit that charges the toner image carried on the intermediate transfer member.   The image forming apparatus according to claim 4, wherein an absolute value of a toner charge amount of the charged toner image is 20 μC / g or more and 40 μC / g or less.   The image forming apparatus according to claim 1, wherein a toner having an average circularity of 0.955 or more and 0.975 or less is used.   The image forming apparatus according to claim 1, wherein a toner having a volume average particle diameter of 4 μm or more and 8 μm or less is used.   The image forming apparatus according to claim 1, wherein a toner containing 0.2 to 3 parts by weight of titanium oxide with respect to 100 parts by weight of the toner is used.