JP4477410B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a color copying machine or a color printer using an electrophotographic system.

  In an image forming apparatus using an electrophotographic system, an electrostatic latent image is formed by exposing a uniformly charged image carrier with light according to image information, and toner as a developer is applied to the image carrier. The electrostatic latent image is supplied and developed, the developed toner image is transferred to a transfer material, and the toner image on the transfer material is heated and fixed to form a recorded image.

  Toner, which is a developer used in an image forming apparatus that employs a fixing method by thermocompression bonding, mainly consolidates each material constituting the toner and fixes the color onto the transfer material, and imparts color to the toner. And a charge control agent for imparting chargeability to the toner. The toner is prepared so as to have a predetermined particle size by mixing these materials simultaneously, melt-kneading, pulverizing the obtained kneaded material, and then classifying.

  The toner used in a full-color copying machine, a color printer, or the like is composed of yellow, magenta, and cyan color toners and black toner, and is created as described above for each colorant to be used.

  In full-color copying machines, color printers, and the like, color toners and black toners are used to form toner images of each color on the surface of a photoreceptor, which is an image carrier, and the toner images are transferred onto a single transfer material such as recording paper. . The recording paper carrying the multiple transferred toner images is conveyed to a fixing device and heated by the fixing device. When heated by the fixing device, the toner forming the toner image is melted, and the toners of the respective colors are mixed and fixed on the recording paper in a state where a specific color is developed.

  In the case of development with full-color toner, a toner image of each color is formed on the surface of the photosensitive member by a developing device. However, since the development position of each color toner is different, a layer of toner of each color is laminated according to image information. A color image is formed. For this reason, depending on the toner layer to be stacked, for example, the first layer toner and the second layer toner formed on the upper layer differ in the way of applying heat, so the second layer toner has sufficient heat. However, heat is not sufficiently transmitted to the toner of the first layer, and the toner of each color may not be sufficiently mixed. As a result, there is a problem that not only a desired color cannot be obtained but also an offset and a fixing defect are likely to occur.

  As a conventional technique for dealing with such a problem, there is a technique in which the softening point temperature of the second developer to be developed later is made lower than the softening point temperature of the first developer (see Patent Document 1). ).

  However, the technique disclosed in Patent Document 1 has the following problems. Setting the softening point temperature of the second developer used for development after the softening point temperature of the first developer to be lower than that of the fixing device, which is a heat source in the image forming apparatus, This means that the second developer having a lower softening point temperature is used in the developing device located closer to the fixing device. In the image forming apparatus, the temperature inside the machine rises due to the radiant heat from the fixing device, and the temperature of the developing device containing the developer also rises. At this time, the developing device provided near the fixing device rises to a higher temperature than the developing device provided far from the fixing device. Therefore, in the technique disclosed in Patent Document 1, the developer having the lower softening point is used in the developing device that rises to a higher temperature.

  In recent years, with the demand for higher image quality, the toner that is a developer component tends to have a smaller particle size, and the small particle size toner has a large specific surface area and thus is easily affected by heat. Therefore, as in Patent Document 1, in a configuration in which a developer having a low softening point is arranged near a fixing device where the temperature is higher, the toner in the developer is easily heated and heated to increase the particle size due to aggregation or the like. Is likely to occur.

  When toner particles are agglomerated and the image formed on the photosensitive member is transferred onto the recording paper by the toner having a large particle size, the transferred image may be blurred or the graininess of the image may be deteriorated. There is a problem that the image quality deteriorates. In the worst case, not only toner aggregation but also toner fusing occurs inside the developing device, resulting in an increase in rotational driving torque of rotating operation parts and the like inside the developing device, and in the developer container of the developing device. Problems such as certain developing tank locking occur. Further, in the case of a two-component developer, there is a problem in that stable toner supply cannot be performed during development due to the occurrence of so-called spent toner fusion to the carrier surface.

Japanese Patent Laid-Open No. 10-186709

  An object of the present invention is to provide an image forming apparatus capable of forming a color image with high quality stably for a long period of time.

  Another object of the present invention is to provide an image forming apparatus capable of stably forming a high-quality image even when the image forming process speed varies depending on the image forming conditions.

The present invention provides an image carrier on which an electrostatic latent image is formed by exposure with light according to image information, and development for developing the electrostatic latent image by supplying toner as a developer to the image carrier. An image forming apparatus comprising: a device; a transfer device that transfers a toner image formed by development onto a transfer material; and a fixing device that heats and fixes the toner image on the transfer material.
There are multiple development devices,
The glass transition point of full color toner in the developer used in each of the plurality of developing devices is different for each developing device,
The glass transition point of the full color toner is 60 ° C. or higher,
Of the plurality of developing devices including the full color toner, the glass transition point of the full color toner in the developer used in the developing device having the shortest separation distance between the fixing device and the developing device, and the separation distance between the fixing device and the developing device. The difference from the glass transition point of the full color toner in the developer used in the longest developing device is within 15 ° C.
When the image forming process speed changes depending on the image forming conditions, the glass transition point of the black toner in the developer used in the developing device that develops the image formed at the changed process speed is used in the remaining developing device. It is set to be higher than the glass transition point of full-color toner in the developer,
The difference between the glass transition point of the black toner and the lowest glass transition point among the glass transition points of the full-color toner is set within 20 ° C.,
An image forming apparatus having a longest separation distance between a developing device including black toner and a fixing device among the plurality of developing devices.

The present invention is also characterized in that the glass transition point of the full-color toner in the developer used in each of the plurality of developing devices is determined according to the separation distance between the fixing device and the developing device.

The present invention is characterized in that the glass transition point of the full-color toner in the developer is set higher as the separation distance between the fixing device and the developing device becomes shorter.

According to the present invention, the image forming apparatus is provided with a plurality of developing devices, and the glass transition point of the full color toner in the developer used in each of the plurality of developing devices is set to be different for each developing device, In particular, the developing device disposed near the fixing device is set so that the glass transition point of the full-color toner in the developer becomes higher. As a result, a full-color toner having a high glass transition point and hardly softening is used in a developing device close to the fixing device as a heat source and having a remarkable temperature rise, so that aggregation in the developing device is prevented and two-component development is performed. The agent prevents spent or the like. Therefore, even in long-term use, any developing device can always stably supply toner for development, and high-quality color image formation is realized by using each color toner in each developing device. be able to.
Further, the difference between the glass transition point of the highest toner and the glass transition point of the lowest toner is set to be within 15 ° C. Thus, for example, when fixing a color toner image formed on a recording paper, each color toner is fixed as a color image that is well mixed and developed into a desired color.
The image forming apparatus is provided with a plurality of developing devices. When the image forming process speed changes depending on the image forming conditions, the image forming apparatus includes a developer used in the developing device for developing an image formed at the changed process speed. The glass transition point of the black toner is set to be higher than the glass transition point of the full color toner in the developer used in the remaining developing device. For example, even in a full-color copying machine or a color printer, a full-color image is not always formed but a monochrome image may be formed. The process speed of monochrome image formation is faster than the process speed of full-color image formation. Therefore, the operating speed of a developing device using black toner is increased during monochrome image formation, so that toner aggregation or spent is likely to occur. I'm left. However, in the present invention, since the glass transition temperature of the black toner is set to be higher than the glass transition temperature of the color toner, the toner can be used even when the developing device operates following a high process speed. Aggregation or spent etc. is prevented.
In addition, since the glass transition point of the black toner is set so that the difference from the lowest glass transition point of the color toners is within 20 ° C., mixing of the black toner and the color toner in fixing during full color image formation Is performed satisfactorily and fixed as a full-color image developed in a desired color.

FIG. 1 is a side view showing a simplified configuration of an image forming apparatus 1 according to an embodiment of the present invention. In this embodiment, a tandem color copier is exemplified as the image forming apparatus 1. The color copying machine 1 is roughly composed of a document table 2, a double-sided automatic document feeder (RADF; Reversing).
Automatic Document Feeder) 3, an image reading unit 4, an image forming unit 5, and a paper feeding unit 6 are provided.

  The document table 2 is a table on which a document serving as original information of an image to be formed is sent and placed. The RADF 3 is supported on the document table 2 so as to be openable and closable with respect to the document table 2, and is mounted on the document placement surface of the document table 2 with a predetermined positional relationship. The RADF 3 first transports the original so that one side of the original faces the image reading unit 4 at a predetermined position on the original table 2, and after the image reading on this one side is completed, the other side is the original table. The document is reversed and conveyed toward the document table 2 so as to face the image reading unit 4 at a predetermined position 2. Further, the RADF 3 discharges the original after completing the double-sided image reading for one original, and executes the double-sided conveyance operation for the next original. The above-described document conveyance and front / back reversing operation by the RADF 3 is controlled in relation to the operation of the entire color copying machine 1.

  The image reading unit 4 is disposed below the document table 2 in order to read an image of the document conveyed on the document table 2 by the RADF 3. The image reading unit 4 includes first and second scanning units 7 and 8 that reciprocate in parallel along the lower surface of the document table 2, an optical lens 9, and a charge coupled device (CCD) line sensor 10.

  The first scanning unit 7 includes an exposure lamp 11 that exposes the image surface of the document, and a first mirror 12 that deflects a reflected light image from the document in a predetermined direction. And reciprocating in parallel at a predetermined scanning speed while maintaining a certain distance. The second scanning unit 8 has second and third mirrors 13 and 14 for deflecting the reflected light image from the original deflected by the first mirror 12 of the first scanning unit 7 in a predetermined direction. The first scanning unit 7 reciprocates in parallel while maintaining a constant speed relationship. The optical lens 9 reduces the reflected light image from the original deflected by the third mirror 14 of the second scanning unit 8 and forms the reduced light image at a predetermined position on the CCD line sensor 10. The CCD line sensor 10 sequentially photoelectrically converts the formed light image and outputs it as an electrical signal. The CCD line sensor 10 is a three-line color CCD that can read a black and white image or a color image and output line data that is color-separated into R (red), G (green), and B (blue) color components. . The document image information converted into an electrical signal by the CCD line sensor 10 is transferred to the image processing unit and subjected to predetermined image data processing.

  The paper feeding unit 6 is disposed below the image forming unit 5 and separates the recording paper P, which is a recording medium stacked and accommodated in the paper tray 15, one by one and supplies the recording paper P toward the image forming unit 5. The recording paper P separated and supplied one by one by the paper supply unit 6 has its leading end detected by a sensor (not shown) and temporarily stopped by a pair of registration rollers 16 based on a detection signal output from this sensor. Further, the timing with the image forming unit 5 is controlled by the registration roller 16 and sent to the transfer conveyance belt 40 that rotates in the direction of the arrow 39. At this time, since the transfer conveyance belt 40 is charged by the charging charger 41, the recording paper P is stably conveyed and supplied by the transfer conveyance belt 40 while passing through the image forming unit 5. Is done. The transfer conveyance belt 40 is an endless belt stretched between the driving roller 42 and the driven roller 43, and is frictionally driven by the driving roller 42 in the direction indicated by the arrow 39 to carry the recording paper P, The images are sequentially conveyed to the image forming unit 5.

  The image forming unit 5 is provided with four first to fourth image forming stations 21b, 21c, 21m, and 21y corresponding to black, cyan, magenta, and yellow. The first to fourth image forming stations 21b, 21c, 21m, and 21y are supplied from the paper supply unit 6 and conveyed from the upstream side to the downstream side in the conveying direction indicated by the arrow 39 of the recording paper P conveyed through the image forming unit 5. Are provided in this order. A fixing device 45 is provided further downstream in the conveyance direction of the recording paper P.

  In the color copying machine 1 of the present embodiment, the first image forming station 21b performs image formation with black toner, the second image forming station 21c performs image formation with cyan toner, and the third image forming station 21m Then, image formation with magenta toner is performed, and the fourth image forming station 21y performs image formation with yellow toner.

  Since the first to fourth image forming stations 21b, 21c, 21m, and 21y have substantially the same configuration, the configuration will be described as a representative of the first image forming station 21b, and the remaining image forming stations. The same reference numerals as those of the first image forming station 21b are attached to the reference numerals, and only the alphabets (cyan; c, magenta; m, yellow; y) representing the toner attached after the reference numerals are changed, and the description thereof is omitted. To do.

  The image forming station 21b includes a laser beam scanner unit 22b and an image forming unit 23b. The laser beam scanner unit 22b is a semiconductor laser element (not shown) that emits dot light modulated according to image data, and a polygon mirror (deflecting device) for deflecting the laser beam from the semiconductor laser element in the main scanning direction. 24b, and fθ lenses 25b1 and 25b2, mirrors 26b1, 26b2, and 26b3 for forming an image of the laser beam deflected by the polygon mirror 24b on the surface of the photoreceptor 27b described later. A pixel signal corresponding to a black component image of a color original image is input to the laser beam scanner unit 22b. The laser beam scanner unit 22b constitutes an exposure unit that irradiates the surface of the photosensitive member 27b with exposure light.

  The image forming unit 23b includes a photoconductor 27b, which is an image carrier that is rotatably supported in the direction of the arrow F around the axis, and the following devices arranged along the circumferential surface of the photoconductor 27b, that is, the above-described devices. A charger 28b that uniformly charges the surface of the photoconductor 27b before being exposed by the laser beam scanner unit 22b, and a surface of the photoconductor 27b formed by exposure of the laser beam output from the laser beam scanner unit 22b. A developing device 29b that develops and visualizes the electrostatic latent image, and a transfer device 30b that transfers the developed image, which is provided facing the photosensitive member 27b via the transfer conveyance belt 40, onto the recording paper P on the transfer conveyance belt 40. And a cleaning device 31b that removes and collects toner remaining on the surface of the photoreceptor 27b after the development processing of the electrostatic latent image. The charger 28b, the developing device 29b, the transfer device 30b, and the cleaning device 31b are provided in this order from the upstream side to the downstream side in the rotation direction indicated by the arrow F.

  The charger 28b uniformly charges the surface of the photoreceptor 27b. The uniformly charged surface of the photoconductor 27b was exposed by the laser beam from the laser beam scanner unit 22b corresponding to the black image information in the original image information, and the charged amount of the exposed portion was not exposed. An electrostatic latent image is formed due to a difference in the charged amount of the part.

  The developing device 29b rotatably supports the developing roller 32b provided facing the photoconductor 27b, a supply roller 33b for supplying a developer to the developing roller 32b, and the developing roller 32b and the supply roller 33b. And a casing 34b for containing a developer containing black toner in the space. By supplying toner from the developing roller 32b of the developing device 29b to the surface of the photoreceptor 27b on which the electrostatic latent image is formed, the electrostatic latent image is developed and visualized. The visualized black toner image is transferred onto the recording paper P on the transfer conveyance belt 40 by the transfer device 30b as described above.

  In the color copying machine 1 of the present embodiment, four first to fourth image forming stations 21b, 21c, 21m, and 21y are provided in this order from the upstream side to the downstream side in the conveyance direction of the recording paper P. In the first image forming station 21b, a black image is formed using black toner provided in the developing device 29b, and in the second image forming station 21c, a cyan color image is formed using cyan toner provided in the developing device 29c. In the image forming station 21m, a magenta image is formed using magenta toner provided in the developing device 29m. In the fourth image forming station 21y, a yellow color image is formed using yellow toner, and full-color document image information is recorded. A full-color toner image is reproduced on the paper P. The full-color toner image on the recording paper P is heated and fixed by a fixing device 45 arranged on the downstream side in the transport direction.

  In the color copying machine 1 according to the present embodiment, the second to fourth image forming stations 21c, 21m, and 21y respectively including color toners (cyan toner, magenta toner, and yellow toner) are fixed to the fourth image forming station 21y. The third image forming station 21m and the second image forming station 21c are arranged in this order.

  One aspect of the present invention is the fourth image formation with the shortest separation distance from the fixing device 45 in the second to fourth image forming stations 21c, 21m, and 21y respectively including color toners (cyan toner, magenta toner, and yellow toner). The second toner image having the highest glass transition point (Tgy) of yellow toner provided in the station 21y, followed by the glass transition point (Tgm) of magenta toner provided in the third image forming station 21m, and the separation distance from the fixing device 45 is the longest. As the glass transition point (Tgc) of cyan toner provided in the forming station 21c becomes the lowest, that is, as the separation distance between the fixing device 45 and the developing device becomes shorter, the glass transition point of the color toner provided becomes smaller. It is set so that it may become high.

  However, it is not preferable to make the glass transition point (Tgy) of yellow toner much higher than the glass transition points (Tgm, Tgc) of other magenta and cyan toners. The reason for this is that if there is too much difference in the glass transition point between color toners, the color toners will not be sufficiently melted and mixed at the time of fixing, making it impossible to control gloss and hue, and fixing images with good color development. It is because it cannot be obtained. Therefore, the difference (= Tgy−Tgc) between the glass transition point (Tgy) of the highest yellow toner and the glass transition point (Tgc) of the lowest cyan toner is set within 15 ° C., preferably within 10 ° C.

  In the present embodiment, the color toner having the lowest glass transition point is a cyan toner, and the glass transition point (Tgc) is preferably 60 ° C. or higher. This is because the glass transition point is preferably 60 ° C. or higher in order to prevent softening and aggregation at the storage environment temperature in consideration of the case where the toner is stored in a supply bottle or the like. Therefore, the glass transition point (Tgy) of the yellow toner set to the highest temperature is set to 75 ° C. or lower, preferably 70 ° C. or lower. Although the glass transition point (Tgc) of cyan toner can be made higher than 60 ° C., if the glass transition point (Tgc) of cyan toner is set high, the glass transition point of the entire color toner increases. This leads to an increase in the fixing set temperature of the fixing device 45 and induces an increase in the temperature inside the color copying machine 1. Therefore, it is preferable to set the glass transition point of the lowest temperature among the color toners to 60 ° C. or higher and as low as possible.

  Another aspect of the present invention is to define the relationship between the glass transition point (Tgb) of the black toner and the glass transition points (Tgc, Tgm, Tgc) of the color toner provided in the first image forming station 21b. is there. When a monochrome image is formed instead of a full-color image, the image forming process speed is increased, and the load on the black toner provided in the first image forming station 21b is increased. When the load on the toner increases, troubles such as toner fusion occur and it is cheap. Therefore, it is preferable to set a glass transition point higher than that of the color toner. In this embodiment, the difference (= Tgb−Tgc) between the glass transition point (Tgb) of the black toner and the glass transition point (Tgc) of the lowest cyan toner among the color toners is within 20 ° C., preferably within 15 ° C. Set to.

As the glass transition point (Tgb) of the black toner is increased, durability against an increase in process speed is increased. However, if the difference in glass transition point between the black toner and the color toner exceeds 20 ° C., the fixing of the full color toner image is performed. At that time, the color toner and the black toner were insufficiently melted and mixed, and a full color image with good color development could not be obtained.
The configuration of each color toner that realizes such a glass transition point will be described later.

  After passing through the first to fourth image forming stations 21b, 21c, 21m, and 21c, the recording paper P on which the toner images of the respective colors are formed is electrostatically attracted to the transfer conveyance belt 40 and further conveyed in the direction of the arrow 39. The The recording paper P is peeled off from the transfer conveyance belt 40 by the discharging device 44 for discharging, which is provided between the fourth image forming station 21 y and the fixing device 45, and sent to the fixing device 45.

  The recording paper P that has passed through the nip formed between the pair of fixing rollers of the fixing device 45 is heated and fixed on the toner image, and reaches the conveyance direction switching gate 46. The conveyance direction switching gate 46 selectively switches between a path for discharging the heat-fixed recording paper P to the outside of the machine body and a path for re-feeding the recording sheet P toward the image forming unit 5. The recording paper P transported again toward the image forming unit 5 by the transport direction switching gate 46 is turned upside down through the switchback transport path 47 and then supplied again to the image forming unit 5, and the image is first printed. An image is formed by repeating the above-described process on the back surface, which is the surface opposite to the formed surface. On the other hand, when the recording paper P is not re-supplied to the image forming unit 5, the recording paper P is sent to the discharge roller 48 by the conveyance direction switching gate 46 and discharged to the discharge tray 49 attached to the outer wall of the machine body by the discharge roller 48. .

  Hereinafter, the toner of the present invention will be described. The toner includes at least a binder resin, a colorant, and a charge control agent.

(Binder resin)
The binder resin used in the toner of the present invention is not particularly limited as long as it is a thermoplastic resin, but is preferably a polyester resin. Since the polyester resin has high charging performance, a good image quality without fogging can be obtained. Polyester resin can maintain high charging performance when combined with a charge control agent, so it is possible to continuously obtain images without image deterioration even during long-term continuous copying, and it is also excellent in transparency, so it is a color toner. Even if it is used for the above, there is an advantage that the saturation and the secondary color reproducibility are not greatly affected.

  The polyester resin can be synthesized from, for example, the following polyhydric alcohol component and polyvalent carboxylic acid component, but the production method is not limited to these. Examples of the polyhydric alcohol component include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 2,3-butanediol, diethylene glycol, triethylene glycol, and 1,5-pentanediol. 1,6-hexanediol, neopentylene glycol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylene Mention may be made of dihydric alcohols such as bisphenol A alkylene oxide adducts such as bisphenol A. Further, a polyhydric alcohol having a valence of 3 or more can also be used in order to make the polymer non-linear to such an extent that no tetrahydrofuran-insoluble matter is generated. Examples of the trivalent or higher alcohol component include glycerin, sorbitol, 1,2,3,6-hexanetetraol, 1,4-sorbitan, pentaerythritol, 1,2,4-butanetriol, 1,2,5-pentane. Examples include triol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene and the like.

  Examples of the polyvalent carboxylic acid component include maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, terephthalic acid, isophthalic acid, cyclohexanedicarboxylic acid, malonic acid, succinic acid, adipic acid, sebacin Examples thereof include dibasic carboxylic acids such as acid, glutaric acid, n-octyl succinic acid and alkyl succinic acid such as n-dodecenyl succinic acid, acid anhydrides and alkyl esters thereof.

  The adjustment of the glass transition point of the color toner and the black toner in the present invention is realized as follows. For example, when a polyester resin is used as the binder resin, the selection and adjustment of the molecular weight component of the polyester resin, the polyester resin and other thermoplastic resins as the binder resin, or other thermoplastic resins may be combined. When used, the glass transition point of each color toner and black toner and the difference in glass transition point between the toners can be set to desired values by adjusting the type and blending ratio of the resin used.

(Coloring agent)
As the colorant used in the present invention, the following can be used. Examples of the colorant for yellow toner include C.I. I. Pigment yellow 1, C.I. I. Pigment yellow 5, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 15, C.I. I. Examples thereof include azo pigments such as CI Pigment Yellow 17, and inorganic pigments such as yellow iron oxide and ocher. For example, C.I. I. Nitro dyes such as Acid Yellow 1 and C.I. I. Solvent Yellow 2, C.I. I. Solvent Yellow 6, C.I. I. Solvent Yellow 14, C.I. I. Solvent Yellow 15, C.I. I. Solvent Yellow 19, C.I. I. Examples thereof include oil-soluble dyes such as Solvent Yellow 21. Among these colorants, C.I. I. Benzidine azo pigments such as CI Pigment Yellow 17 are preferably used in terms of color as a yellow colorant.

  Examples of the colorant for magenta toner include C.I. I. Pigment red 49, C.I. I. Pigment red 57, C.I. I. Pigment red 81, C.I. I. Pigment red 122, C.I. I. Solvent Red 19, C.I. I. Solvent Red 49, C.I. I. Solvent Red 52, C.I. I. Basic Red 10, C.I. I. Disperse Red 15 etc. are mentioned. In particular, C.I. I. A quinacridone pigment such as CI Pigment Red 122 is preferably used in terms of color as a magenta colorant.

  Examples of the colorant for cyan toner include C.I. I. Pigment blue 15, C.I. I. Pigment blue 16, C.I. I. Solvent Blue 55, C.I. I. Solvent Blue 70, C.I. I. Direct Blue 25, C.I. I. Direct blue 86 etc. are mentioned. In particular, C.I. I. A copper phthalocyanine pigment such as CI Pigment Blue 15 is preferably used in terms of color as a cyan colorant.

  Carbon black is preferably used as the colorant for black toner. Examples of carbon black include channel black, roller black, disk black, gas furnace black, oil furnace black, thermal black, acetylene black, and the like, and may be appropriately selected from these known carbon blacks.

(Charge control agent)
As the toner charge control agent, a metal complex of salicylic acid is used. The metal complex of salicylic acid is stable as a compound and has good charge stability of the toner, and is monochromatic or colorless and has little influence on the color, so that it can be used for a color toner. Further, from the viewpoints of environmental safety, insufficient charging effect, reverse charging of the toner, dispersibility and stability of the compound itself, a zirconium salicylate compound described in International Publication No. WO99 / 12941 is preferably used.

  The content of the charge control agent is preferably 0.5 to 3 parts by weight with respect to 100 parts by weight of the binder resin. If it is less than 0.5 part by weight, sufficient charging stability cannot be obtained. On the other hand, when the amount exceeds 3 parts by weight, dispersibility deteriorates and charging stability in long-term running is lacking, so that an image with stable quality cannot be obtained. Furthermore, since the probability that the charge control agent is present on the toner surface increases, charging failure occurs in a high humidity environment, and background fogging occurs. Further, when used for color toners, if a dispersion type charge control agent is used, the transparency of the toner is lowered, so that the saturation is lowered and the color development such as secondary color and tertiary color is lowered.

(Release agent)
The toner of the present invention may contain a wax as a release agent. For wax, natural beeswax, whale wax, shellac wax, plant-derived carnauba wax, wood wax, rice bran wax (rice wax), candelilla wax, petroleum-derived paraffin wax, microcrystalline wax, mineral-derived Examples of synthetic waxes include Fischer-Tropsch wax, polyethylene wax, oil-based synthetic waxes (esters, ketones, amides), hydrogenated waxes, and the like. The type of the wax used as the release agent is not particularly limited.

  The toner of the present invention is not particularly limited in its production method, but is preferably produced using a pulverization method in which the additives contained in the toner such as a charge control agent are relatively easy to disperse. In the pulverization method, additives such as the above-mentioned binder resin, colorant, charge control agent, and release agent are premixed by a dry blender, Henschel mixer, ball mill, or the like so that the mixture is uniformly mixed. In this method, toner particles are produced by melt-kneading, then cooling and pulverizing the kneaded product, and classifying as necessary.

  The melt kneading is preferably performed with an open roll kneader. The open roll type kneader is formed so that the gap width between both rolls arranged to face each other gradually narrows from the supply side of the raw material mixture toward the discharge side. By forming the gap in this way, the compressive force of the roll acting on the raw material mixture increases from the supply side to the discharge side, so that the dispersibility of the additive in the kneaded product obtained can be improved.

  In the toner of the present invention, the toner particles obtained by pulverization or classification after pulverization preferably have an average particle diameter of 3 μm to 15 μm. In particular, in order to obtain a high-quality image, a small particle toner having an average particle diameter of 9 μm or less, preferably 5 μm to 8 μm is used.

  The toner of the present invention can be used as a two-component developer by combining with a carrier. When used as a two-component developer, the toner particles may be surface-treated with hydrophobic inorganic fine particles in order to stabilize the stirrability, transportability and chargeability of the toner with respect to the carrier. Examples of the hydrophobic inorganic fine particles include inorganic fine particles subjected to hydrophobic treatment such as aluminum oxide powder, titanium oxide powder, and fine powder silica, and these can be used alone or in combination. Further, the hydrophobic inorganic fine particles can be used in combination with external additives such as vinylidene fluoride fine powder, polytetrafluoroethylene fine powder, fatty acid metal salt, zinc stearate, calcium stearate and the like. The toner is manufactured by adding these inorganic fine particles and / or resin fine particles as external additives, and then removing aggregates and foreign matters with a sieve or the like.

(Career)
Examples of the carrier core material include magnetic metals such as iron, nickel, and cobalt, magnetic metal oxides such as ferrite and magnetite, and glass beads. Moreover, the particle diameter of the core is generally 10 to 500 μm, preferably 30 to 100 μm.

  The carrier is preferably a resin-coated carrier having a resin coating layer on the core material. Further, a conductive material may be dispersed in the resin coating layer. Examples of the resin used for forming the resin coating layer include polyethylene, polypropylene, polystyrene, polyacrylonitrile, polyvinyl acetate, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene. Examples include, but are not limited to, acrylic acid copolymers, silicone resins composed of organosiloxane bonds or modified products thereof, fluororesins, polyesters, polyurethanes, polycarbonates, phenol resins, amino resins, melamine resins, benzoguanamine resins, etc. is not. Examples of the conductive material contained in the resin coating layer include, but are not limited to, metal powders such as gold, silver, and copper, and inorganic fine particles such as carbon black, titanium oxide, and zinc oxide.

  As described above, in the image forming apparatus 1 according to the present embodiment, the exposure of the photosensitive member in the image forming station is performed by scanning the laser beam, but the present invention is not limited to this. A configuration in which a writing optical system (LED head) including an imaging lens array is used may be used. The LED head is smaller than the laser beam scanner unit and has no moving parts and is silent. Therefore, it can be suitably used in an image forming apparatus such as a tandem digital color copying machine that requires a plurality of optical writing units.

1 is a side view showing a simplified configuration of an image forming apparatus 1 according to an embodiment of the present invention.

Explanation of symbols

1 Image forming apparatus 2 Document table 3 RADF
4 Image Reading Unit 5 Image Forming Unit 6 Paper Feeding Unit 21 Image Forming Station 22 Laser Beam Scanner Unit 23 Image Forming Unit 27 Photosensitive Member 29 Developing Device

Claims (3)

An image carrier on which an electrostatic latent image is formed by exposure with light according to image information, a developing device for developing the electrostatic latent image by supplying toner as a developer to the image carrier, and development An image forming apparatus comprising: a transfer device that transfers a toner image formed thereon to a transfer material; and a fixing device that heats and fixes the toner image on the transfer material.
There are multiple development devices,
The glass transition point of full color toner in the developer used in each of the plurality of developing devices is different for each developing device,
The glass transition point of the full color toner is 60 ° C. or higher,
Of the plurality of developing devices including the full color toner, the glass transition point of the full color toner in the developer used in the developing device having the shortest separation distance between the fixing device and the developing device, and the separation distance between the fixing device and the developing device. The difference from the glass transition point of the full color toner in the developer used in the longest developing device is within 15 ° C.
When the image forming process speed changes depending on the image forming conditions, the glass transition point of the black toner in the developer used in the developing device that develops the image formed at the changed process speed is used in the remaining developing device. It is set to be higher than the glass transition point of full-color toner in the developer,
The difference between the glass transition point of the black toner and the lowest glass transition point among the glass transition points of the full-color toner is set within 20 ° C.,
An image forming apparatus having a longest separation distance between a developing device including black toner and a fixing device among the plurality of developing devices. The glass transition point of the full-color toner in the developer used in each of the plurality of developing devices is
The image forming apparatus according to claim 1, wherein the image forming apparatus is determined according to a separation distance between the fixing device and the developing device.   3. The image forming apparatus according to claim 2, wherein the glass transition point of the full-color toner in the developer is set higher as the separation distance between the fixing device and the developing device becomes shorter.

Images