JP2001272866A - Image forming method and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method and an image forming apparatus capable of stably forming a high-quality image with little density irregularity and little transfer omission without causing the lowering of image forming speed and the increase of energy consumption and making the device larger and cost higher even when forming a high-resolution digital image on a variety of paper having different surface shape. SOLUTION: By heating and melting a toner image formed on an intermediate transfer belt 5, bringing the desired paper 8 into contact with the belt 5 through the toner image and applying pressure to the back surface of the paper 8, the toner image on the belt 5 is transferred and fixed simultaneously on the paper 8 in this image forming method. Before heating the toner image after bringing the paper 8 into contact with the belt 5, the toner image on the belt 5 is previously moved to the paper 8 by a corotron 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an image comprising a fixed toner image on a recording medium by forming a toner image and finally transferring and fixing the formed toner image on a predetermined recording medium. The present invention relates to an image forming method and an image forming apparatus such as a printer or a copier employing the image forming method.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus using a thermoplastic toner, an electrophotographic image forming apparatus is representative. An electrophotographic image forming apparatus forms an electrostatic latent image on a photoconductor in accordance with an image signal, develops the electrostatic latent image with toner to form a toner image on the photoconductor,
Further, the toner image is electrostatically transferred to a desired sheet, and the transferred toner image is heated and fixed on the sheet.

In recent years, with the development of computers, generalization of color displays, maintenance of communication networks, and the emergence of large-capacity storage media, scanners and digital cameras have become widespread, and high-quality color image output devices are expected. As a result, color electrophotographic apparatuses have been actively developed. 2. Description of the Related Art A color electrophotographic apparatus forms a color image by forming color-separated toner images of black, yellow, magenta, and cyan, and sequentially superimposing and transferring the toner images of each color onto a transfer-receiving medium. is there.

[0004] In a color electrophotographic apparatus, an image centered on a gray scale expression is centered compared to a monochromatic image centered on a character or line image in a conventional black-and-white electrophotographic apparatus. Have very high demands. However, in actuality, the toner layer thickness is increased due to the superposition of the toner images of each color, and as a result, toner scattering and transfer unevenness in the toner image transfer portion become remarkable, and the image quality is easily deteriorated. Holding a point.

In the electrostatic transfer type image forming apparatus, the transfer efficiency of the toner image increases in proportion to the strength of the electric field applied to the toner layer. Therefore, when the electric field intensity fluctuates due to unevenness in the thickness of the toner layer, unevenness on the surface of the paper, and unevenness in electrical properties, the transfer efficiency also fluctuates, resulting in transfer unevenness. Further, if the transfer electric field is simply increased, a so-called Paschen discharge occurs, and the intensity of the electric field applied to the toner layer is reduced, or a part of the toner is charged to the opposite polarity, and the transfer efficiency is rather reduced. . Therefore, the transfer efficiency shows a peak at a certain electric field value, and the peak of the efficiency of electrostatic transfer generally does not reach 100%.
The maximum is about 95%, usually about 80%.

In an image forming apparatus of the type in which a toner image formed on a photoreceptor is directly transferred to a sheet, the intensity of an electric field fluctuates mainly due to unevenness of the surface of the sheet and unevenness of electric properties, and transfer unevenness occurs. . The paper has not only unevenness in its own electrical properties, but also high hygroscopicity, and the electrical resistance value greatly varies depending on the amount of moisture absorption. In addition, various types of paper are used, and plain paper and rough paper having large surface irregularities are often used in office and personal use, and the transfer efficiency is largely fluctuated by the surface irregularities. Further, when the toner images of each color formed separately are transferred onto a sheet in a superimposed manner, the above-mentioned transfer unevenness occurs every time the toner image of each color is transferred, and the accumulated unevenness causes the density unevenness to be remarkable. Therefore, it is difficult to stably form a high-quality image.

On the other hand, using an intermediate transfer medium whose surface shape and electrical properties are controlled, toner images of each color separately formed on a photoreceptor are primarily transferred so as to be superimposed on the intermediate transfer medium. In a so-called intermediate transfer type image forming apparatus, in which a multicolor toner image formed on an intermediate transfer medium is secondarily transferred to paper, the transfer efficiency of the primary transfer is small, and the transfer efficiency is smaller than that of an image directly transferred to paper. A good image with less unevenness can be obtained.

However, when an intermediate transfer medium is used, a secondary transfer of transferring a multicolor toner image formed on the intermediate transfer medium to a sheet becomes a serious problem. In the secondary transfer,
The multi-color toner image formed on the intermediate transfer medium is affected by the unevenness of the surface of the paper and the unevenness of the electrical properties as described above. Since the thickness varies greatly, it is extremely difficult to apply a constant electric field to the toner image.

Therefore, in an electrophotographic image forming apparatus using an intermediate transfer medium, a secondary transfer of a multicolor toner image, which is primarily transferred on the intermediate transfer medium and has little density unevenness, to a sheet as it is, causes a secondary transfer. Eventually, transfer unevenness occurs and image quality deteriorates. In particular, since the transfer unevenness in the secondary transfer is strongly influenced by the thickness of the toner layer on the intermediate transfer medium, the color balance of the color image transferred on the paper is largely shifted, and a desired color image is obtained. Is difficult.

[0010] In response to such a problem,
No. 41679 discloses that a toner image formed on a photoreceptor is adhesively transferred to the surface of an intermediate transfer belt having elasticity, and then, using a heating roller, a sheet supplied between the intermediate transfer belt and the heating roller is used. There is disclosed an image forming method in which an intermediate transfer belt is heated, a toner image on the intermediate transfer belt is heated and melted, and the image is thermally transferred onto a sheet. in this way,
Since the transfer of the toner image from the intermediate transfer belt to the sheet is performed in a non-electrostatic manner, the image quality in the electrostatic transfer system as described above hardly deteriorates.

Japanese Patent Application Laid-Open No. 51-94939 discloses a multicolor toner image formed on an intermediate transfer drum by primary-transferring a plurality of color toner images so as to be electrostatically superimposed on the intermediate transfer drum. An image forming apparatus is disclosed in which a multi-toner image is secondarily transferred onto a sheet by heating and fusing the image and then pressed against the sheet, and simultaneously fixed to obtain a color image. Also in the image forming apparatus employing such a simultaneous transfer fixing method, since the toner image is transferred to the sheet in a non-electrostatic manner, the deterioration of the image quality in the above-mentioned electrostatic transfer method rarely occurs.

Japanese Patent Application Laid-Open Nos. Hei 5-196442 and Hei 5-249798 disclose a technique in which these simultaneous transfer fixing methods are partially improved. In these publications, in order to completely transfer the toner image from the toner image carrier to the paper, the toner image carrier and the paper are heated and pressed to transfer the toner image onto the paper, and then the toner An image forming method is disclosed in which the sheet is conveyed in a contact state and cooled until the cohesive force becomes larger than the adhesive force between the toner and the intermediate transfer medium, and then the sheet is separated from the intermediate transfer medium.

In Japanese Patent Application Laid-Open No. 5-6059, a dielectric belt is used in place of a photoreceptor, an electrostatic latent image is formed on the dielectric belt by an ion recording head, and the electrostatic latent image is developed to form a toner. An image forming apparatus is disclosed in which after forming an image, the toner image is heated from the back surface of the dielectric belt and the sheet is pressed against the sheet to transfer and fix the toner image onto the sheet at the same time.

FIG. 10 is a schematic structural view of a conventional image forming apparatus employing the simultaneous transfer and fixing method.

In the image forming apparatus 500, photosensitive drums 1Y and 1M which rotate in the direction of arrow A shown in the figure corresponding to each color of yellow, magenta, cyan, and black on which an electrostatic latent image is formed on the surface. , 1C, 1K, and the photosensitive drum 1
Chargers 2Y, 2 for uniformly charging Y, 1M, 1C, 1K
M, 2C and 2K are provided.

Further, the image forming apparatus 500 irradiates the exposure light 3Y, 3M, 3C, 3K corresponding to the image of each color onto the surface of each of the photosensitive drums 1Y, 1M, 1C, 1K.
An image exposure device (not shown) for forming an electrostatic latent image on each of the photosensitive drums 1Y, 1M, 1C and 1K, and an electrostatic latent image formed on each of the photosensitive drums 1Y, 1M, 1C and 1K Are developed with toner of each color to form toner images of each color, and an intermediate transfer belt 5 circulating and moving in the direction of arrow B shown in the figure.

Further, in the image forming apparatus 500, primary transfer means 6Y, 6M, 6C, 6K for transferring the respective color toner images on the photosensitive drums 1Y, 1M, 1C, 1K to the intermediate transfer belt 5 so as to overlap each other. And a heating roll 11 for heating the multicolor toner image superimposed and transferred on the intermediate transfer belt 5
And a pressure roll 12 that presses the fused multicolor toner image with the sheet 8 so as to sandwich the fused multicolor toner image therebetween, and a cleaning unit 13Y that removes toner remaining on the photosensitive drums 1Y, 1M, 1C, and 1K. , 13M, 13C, 13K,
A belt cleaning unit 14 that removes toner and paper dust remaining on the intermediate transfer belt 5 and a cooling unit 15 that cools the toner image on the sheet 8 on which the heat transfer and fixing have been performed are provided.

In the image forming apparatus 500, the multicolor toner image formed on the intermediate transfer belt 5 is heated and melted by the heating roll 11, and the paper 8 is melted on the intermediate transfer belt 5 by the pressure roll 12. By bringing the toner image into close contact with the formed toner image, the melted toner image is adhered to the sheet 8 and further cooled by the cooling unit 15 until the toner image is sufficiently adhered to the sheet 8. In this way, the toner image is transferred onto the sheet 8 and fixed.

[0019]

However, the image forming apparatus employing the above-described non-electrostatic transfer simultaneous fixing method has the following problems.

There are two types of electrophotographic image forming apparatuses, an analog type and a digital type. Recently, a digital type image forming apparatus capable of more stably obtaining a high quality image has been used. It is becoming more and more used. In a digital image forming apparatus, character data or image data is given as binary information of ON and OFF as two-dimensional information for a predetermined location on a toner image carrier. As a method of recording a halftone image using the binary information, there are a halftone dot structure in which the gradation is expressed by changing the dot size, and a line structure in which the gradation is expressed by changing the line thickness. Area modulation method. Such a method has been adopted in many digital image forming apparatuses because the algorithm is relatively simple and the cost is low.

The present inventor has adopted the above-described simultaneous transfer and fixing method by heat in a digital image forming apparatus for forming a halftone image by an area modulation method using a halftone dot structure or a line structure as described above. As a result of repeated image forming tests, it was confirmed that there was a serious problem that an image in a low density portion and fine lines and fine characters were missing without being transferred.

This is due to the state of contact between the toner image and the paper, and is due to the structure of the toner image formed on the toner image carrier and the surface shape of the paper. The simultaneous transfer and fixing method using heat employed in the above-described conventional image forming apparatus includes:
The toner image carrier and the sheet are brought into close contact with each other with the toner image interposed therebetween, and the heat-fused toner image is attached to the sheet. After cooling the toner image, the toner image carrier and the sheet are separated.

FIG. 11 is a view showing the state of transfer of a toner image based on the magnitude relationship between the adhesion between toner and paper, the cohesion between toners, and the adhesion between toner and a toner image carrier.

FIG. 11A shows a state in which the toner image carrier 102 and the sheet 8 are in close contact with the toner image 101 therebetween. 11 (b), 11 (c) and 11 (d) show the transfer state of the toner image 101 based on the magnitude relationship of the respective forces when the sheet 8 is peeled from this state.
Respectively. Here, the adhesive force between the toner 101a and the paper 8 is Fp, the cohesive force between the toners 101a is Ft, and the adhesive force between the toner 101a and the toner image carrier 102 is Fr. FIG. 11B shows that Fr <Fp and F
A state in which a force relationship of r <Ft is established is shown. In this state, the toner 101a adheres to the sheet 8. FIG. 11C shows that Ft <Fr and Ft <
The state where the force relationship of Fp is established is shown. In this state, the toner 101a is
And paper 8. Further, FIG.
Shows a state where the force relations of Fp <Fr and Fp <Ft are established. In this state, the toner 1
01a adheres to the toner image carrier 102.

As is apparent from FIG. 11B, Fr <
When the force relationship of Fp and Fr <Ft is established, the toner 101 a
Then, transfer and fixing are simultaneously achieved.

Generally, the cohesive force Ft of the thermally fused toner 101a is large, and if the toner 101a is cooled to a predetermined temperature,
r <Ft and Fp <Ft hold. Further, Fr can be reduced by performing processing so as to increase the releasability of the toner 101a from the surface of the toner image carrier 102, so that Fr <Fp can be realized relatively easily. However, when the toner image 101 and the sheet 8 are brought into close contact with each other with the toner image 101 sandwiched therebetween, if the toner image 101 and the sheet 8 do not sufficiently contact each other, Fr> Fp, and the toner image 101 is That is, it is not transferred to the image carrier 102 and remains on the image carrier 102.

Here, the relationship between the structure of the toner image formed on the toner image carrier and the shape of the paper surface is increasing. In recent years, the resolution of digital images has been increased with the aim of improving the image quality. Line (line / inch) or 120
0 dpi (dot / inch) is becoming mainstream.
When an image is formed with these resolutions, it is necessary to form very fine pixels having a minimum dot diameter of 20 μm to 30 μm or less in a halftone dot image and a line width of 20 μm to 30 μm or less in a line image. become. Also, in order to realize higher resolution, the toner particle size has been reduced,
At present, toner of about 7 μm to 10 μm is used, and the height of a toner image is about 10 μm to 20 μm for a single color and about 30 μm to 60 μm for three colors. On the other hand, the unevenness of the paper surface is such that the depth of
Although it is about 5 μm, the one usually used as plain paper has a concave portion having a depth of about 5 to 20 μm, and in the case of recycled paper or rough paper, the concave portion has a depth exceeding 30 μm in some cases. The size of the concave portion ranges from a small size of about several μm to a size exceeding 100 μm.

FIG. 12 is a diagram schematically showing pixels of a high-resolution toner image formed on a toner image carrier, a surface shape of a sheet, and a state of thermal transfer fixing.

FIG. 12A shows the toner image carrier 102.
A state in which the toner image 101 formed thereon is thermally transferred and fixed to the smooth paper 8_1 and peeled off is shown. FIG.
FIG. 2B shows a state in which the toner image 101 formed on the toner image carrier 102 is thermally transferred and fixed to the plain paper 8_2 and peeled off. Further, in FIG.
Toner image 101 formed on toner image carrier 102
However, a state where the sheet is thermally transferred and fixed to the rough paper 8_3 and peeled off is shown. As can be seen from these figures, when paper with large surface irregularities is used, in areas corresponding to low-density areas, fine lines, and fine character details in monochrome images, pixels where the toner image and paper only partially touch Pixels that do not occur. Accordingly, the above-described force relationship (Fr <Fp)
Is not satisfied, and the toner comes off without being transferred to the paper.

As a method for solving this problem, it is also possible to form an elastic layer on the toner image carrier and deform the elastic layer along the surface irregularities of the paper by applying pressure to enhance the adhesion between the toner image and the paper. However, for that purpose, an elastic layer having a thickness of several tens of μm or more must be formed on the toner image carrier. However, when such a thick toner image carrier is used, a large amount of energy is required to heat the toner image carrier, and the energy consumption becomes extremely large. In addition, since there are few elastic members having high thermal conductivity in the world, such elastic members are rarely used, so that it takes time for heat from a heat source to heat the toner image via the toner image carrier. Therefore, there is a problem that an image cannot be continuously formed at a high speed.

It is also possible to deform the surface of the paper by applying a very high pressure to increase the adhesion between the toner image and the paper. It is necessary to use a heat roll or the like in which a thick metal pipe is used for the core, so that the heat capacity of the heating member increases and the time for warming up becomes very long. In addition, there is a large problem that the supporting member and the like become large-scale so as to endure a high load, and it is unavoidable to increase the size, weight, and cost of the apparatus.

The present invention has been made in view of the above circumstances, and even when a high-resolution digital image is formed on various sheets having different surface shapes, the image forming speed is reduced, the energy consumption is increased, and the size of the apparatus is increased. It is an object of the present invention to provide an image forming method and an image forming apparatus capable of stably forming a high-quality image with less density unevenness and transfer omission without increasing cost.

[0033]

According to the image forming method of the present invention, which achieves the above object, a toner image is formed, and the formed toner image is finally transferred and fixed onto a predetermined recording medium. In an image forming method for forming an image composed of a fixed toner image on a recording medium, a toner image carrier for carrying a toner image and a recording medium are sandwiched between the toner image carried on the toner image carrier. And applying a force in a direction in which the toner image is transferred from the toner image carrier to the recording medium to the toner image on the toner image carrier in a state where the recording medium is superimposed. A pre-transfer process for performing pre-transfer,
After completion of the pre-transfer process, the toner image carrier and the recording medium in a superimposed state are heated and further pressed to transfer and fix the toner image from the toner image carrier to the recording medium. And a transfer fixing step.

Here, it is preferable that the preliminary transfer step is a step of applying an electrostatic force to the toner image.

The image forming apparatus of the present invention that achieves the above object forms a toner image, and finally transfers and fixes the formed toner image on a predetermined recording medium, so that the image is formed on the recording medium. In an image forming apparatus that forms an image composed of a fixed toner image, a predetermined toner image carrier,
A toner image forming means for carrying a toner image on the toner image carrier, and a recording medium conveyed on the toner image carrier with the toner image carried on the toner image carrier interposed therebetween Recording medium conveying means, and the toner on the toner image carrier in a state where the recording medium is superimposed at a predetermined preliminary transfer position in the middle of being conveyed in a state where the toner image carrier and the recording medium are superimposed. In the statue,
A pre-transfer unit for applying a force in the direction in which the toner image is transferred from the toner image carrier to the recording medium; and Transfer and fixing means for transferring and fixing the toner image from the toner image carrier to the recording medium by heating and pressurizing the toner image carrier and the recording medium in a state where the toner image carrier is in a state of being pressed. I do.

Here, it is preferable that the preliminary transfer means applies an electrostatic force to the toner image.

In a preferred embodiment, the apparatus further comprises a vibration applying means for vibrating the toner image carrier and the recording medium during the preliminary transfer by the preliminary transfer means.

Further, it is preferable that the image forming apparatus further comprises a charge applying means for applying to the toner image carried on the toner image carrier before the recording medium is superposed a charge having a polarity which assists the preliminary transfer by the preliminary transfer means. It is.

A surface shape measuring means for measuring the surface shape of the recording medium before the image is recorded, and whether or not the preliminary transfer means is operated based on the measurement result by the surface shape measuring means. A preliminary transfer control unit may be provided.

[0040]

Embodiments of the present invention will be described below.

FIG. 1 is a schematic configuration diagram of a first embodiment of the image forming apparatus of the present invention.

The image forming apparatus 100 shown in FIG. 1 is provided with photosensitive drums 1Y, 1M, 1C, and 1K corresponding to yellow, magenta, cyan, and black, respectively. These photosensitive drums 1Y, 1M, 1C, 1K rotate in the direction of arrow A shown in FIG.

The image forming apparatus 100 includes a charger 2 for uniformly charging the photosensitive drums 1Y, 1M, 1C, and 1K.
Y, 2M, 2C, and 2K, and each photosensitive drum 1Y, 1M,
1C, 1K spot light 3 according to the image signal of each color
Y, 3M, 3C, and 3K are irradiated to each photosensitive drum 1Y,
An image exposure device (not shown) for forming an electrostatic latent image of each color on 1M, 1C, 1K, and a photosensitive drum 1Y, 1M, 1C, 1K on which the electrostatic latent image has been formed, are arranged in yellow, magenta, Each of the color developing units 4Y, which develop using cyan and black color toners,
4M, 4C, and 4K, and each of the photosensitive drums 1Y, 1M, and 1
And an intermediate transfer belt 5 to which a toner image formed on C and 1K is primarily transferred.

Further, in the image forming apparatus 100, each of the primary transfer means 6Y, 6M, 6E, 6M, which electrostatically transfers the toner images on each of the photosensitive drums 1Y, 1M, 1C, 1K so as to be superimposed on the intermediate transfer belt 5. 6C and 6K, and the intermediate transfer belt 5
The roll member 7 that bridges the intermediate transfer belt 5
There is provided a paper transporting unit 9 for transporting the paper 8 in a superposed manner so as to sandwich the toner image electrostatically transferred onto the intermediate transfer belt 5 therebetween.

In the image forming apparatus 100, at a predetermined pre-transfer position where the intermediate transfer belt 5 and the sheet 8 are conveyed in a superimposed state, the intermediate transfer belt in which the sheet 8 is superimposed is provided. A corotron 10 is provided to apply a force in a direction in which the toner image is transferred from the intermediate transfer belt 5 to the sheet 8 to the toner image on the sheet 5.
Specifically, the corotron 10 applies an electrostatic force to the toner image.

Further, the image forming apparatus 100 heats the superposed intermediate transfer belt 5 and the sheet 8 in the conveying direction of the sheet 8 by the sheet conveying means 9 on the downstream side of the preliminary transfer position. A transfer / fixing unit including a heating roll 11 and a pressure roll 12 for transferring and fixing the toner image from the intermediate transfer belt 5 to the paper 8 by further pressing is provided.

The image forming apparatus 100 includes, if necessary, the photosensitive drum 1 after the primary transfer of the toner image.
Cleaning means 13Y, 13M, 13C, 13K for removing the toner remaining on Y, 1M, 1C, 1K, and toner and paper dust remaining on the intermediate transfer belt 5 after the toner image is transferred onto the paper 8. There are provided a belt cleaning unit 14 for removal, an intermediate transfer belt 5 closely contacting the toner image after the thermal transfer fixing, and a cooling unit 15 for cooling the sheet 8.

Here, the image forming apparatus 100 of the present embodiment
Is equivalent to the toner image carrier in the present invention, and the photosensitive drums 1Y, 1M,
The means from the formation of the toner image on 1C and 1K to the transfer to the intermediate transfer belt 5 corresponds to the toner image forming means according to the present invention. Further, the corotron 10 corresponds to a pre-transfer unit in the present invention.

As the photosensitive drums 1Y, 1M, 1C, 1K, a general photosensitive drum in which an organic or inorganic photoconductive layer is formed on a conductive drum such as aluminum can be used.

As the toner, a known toner composed of a transparent thermoplastic resin containing dyes of each color can be used. In the present embodiment, a dispersion in which each color pigment and a charge control agent are dispersed using a polyester resin as a binder is used. The average particle diameter of the toner is about 7 μm in consideration of image quality and handling.
The charge polarity of the toner used in the present embodiment is negative.

The intermediate transfer belt 5 in this embodiment is
In consideration of electrostatic primary transfer and secondary transfer by heating,
A belt having a two-layer structure including a base layer and a surface layer is used. For the base layer, a polyimide resin whose electric resistance value was adjusted to 10 ⁷ Ω · cm to 10 ¹⁰ Ω · cm by adding a conductive tin oxide filler was used. And In addition to this, any other material having high heat resistance can be used as the base layer.
For example, polyester, polyethylene terephthalate,
Polymer sheets such as polyethersulfone, polyetherketone, polysulfone, polyimide, polyimideamide, and polyamide, and metals such as SUS and Ni can be used.

For the surface layer, a 5 μm thick silicon copolymer is used. Since the silicone copolymer has a property of easily separating from the toner which has been melted and fluidized by heat, it is suitable for efficiently transferring the toner image from the intermediate transfer belt 5 to the paper 8. In addition, the following materials having high releasability can be used for the surface layer in addition to the silicon copolymer. For example, a tetrafluoroethylene_perfluoroalkylvinyl ether copolymer, polytetrafluoroethylene, or the like can be used.

In this embodiment, a bias transfer roll is used as the primary transfer means 6. This bias transfer roll is formed by coating a metal roll with polyurethane rubber whose electric resistance is controlled to 10 ⁶ Ω · cm to 10 ⁸ Ω · cm. This bias transfer roll is brought into contact with the back surface of the intermediate transfer belt 5 with a load of about 9.8 N (1 kgf), and
A positive voltage of V to 2 kV is applied. Note that the primary transfer in the present embodiment is the transfer of the toner image from the photosensitive drums 1Y, 1M, 1C, 1K to the intermediate transfer belt 5. As described above, the surface shape and electrical characteristics of both are sufficiently controlled. Thus, electrostatic transfer with less unevenness and disturbance can be performed.

As a pre-transfer means, a corotron 1 for generating aerial ions by applying a high voltage to the electrode wire and causing a corona discharge between the electrode wire and the shield member.
0, and set it on the back of the paper 8. Since the toner used in the present embodiment is negatively charged, a voltage of +6 kV is applied to the electrode wires to apply a positive charge to the back surface of the paper 8. Incidentally, the corotron 10 may be arranged on the back surface of the intermediate transfer belt 5 so as to apply a negative charge of the same polarity as the toner to the back surface of the intermediate transfer belt 5.

As the heating roll 11, a metal roll having a heat source such as a halogen lamp disposed therein, or a metal roll having a heat-resistant elastic layer such as silicon rubber formed on the surface thereof can be used. In the present embodiment, a halogen lamp having a rated power of 650 W is used as a heat source. A stainless steel pipe having a diameter of 30 mm and a thickness of 0.5 mm is used for the roll member. The temperature of the heating roll 11 is set at about 120 ° C. to about 200 ° C. so that the toner is softened as necessary.

The pressure roll 12 is the same as the heating roll 1 described above.
The same configuration as that of 1 can be used. In this embodiment, in order to apply pressure more uniformly in the axial direction, 0.5 mm is applied to a stainless steel pipe having a diameter of 30 mm and a thickness of 1 mm.
One having a silicon rubber layer having a thickness of mm is used.
Note that a heat source such as a halogen lamp may be disposed inside the pressure roll 12 to heat the paper 8 from the back side.

The pressure roll 12 is provided with a pressure mechanism for pressing the paper 8 and the intermediate transfer belt 5 against the heating roll 11.
2 is pressed against the heating roll 11 with a load of 49 N to 196 N (5 kgf to 20 kgf).

Cleaning means 13Y, 13M, 13
For C and 13K, rubber hardness is about 60 degrees and thickness is 2mm
Is used. The blade comes into contact with the photosensitive drums 1Y, 1M, 1C, and 1K, and the toner remaining on the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K is removed. In addition, a brush-shaped roll member or the like can be used.

A similar blade is used for the belt cleaning means 14. Since the intermediate transfer belt 5 used in the present embodiment has excellent releasability from the toner, the residual toner can be sufficiently scraped off by the blade. In addition, a heating roller having a surface coated with a resin material similar to that of the toner binder may be used, and the remaining toner may be adhered to the roll surface while being heated and removed. The belt cleaning means 14 is configured such that the pressing mechanism is retractable, and while forming the toner images of the respective colors on the intermediate transfer belt 5, the belt cleaning means 14 is retracted to the retract position so that the intermediate transfer belt 5 Be separated. Further, after the formation of the multicolor toner image on the intermediate transfer belt 5 and the transfer to the paper 8 are completed, it is set at a position where it is pressed against the intermediate transfer belt 5.

Returning to FIG. 1, the image forming method according to the present embodiment will be described. This image forming method has a superimposing step of superimposing an intermediate transfer belt 5 carrying a toner image and a sheet 8 such that the toner image carried on the intermediate transfer belt 5 is sandwiched therebetween. Preliminary transfer in which preliminary transfer is performed by applying a force in the direction in which the toner image is transferred from the intermediate transfer belt 5 to the paper 8 to the toner image on the intermediate transfer belt 5 in a state where the paper 8 is superimposed. Having a process. Further, after the completion of the preliminary transfer process, the intermediate transfer belt 5 and the sheet 8 in a superimposed state are heated and further pressed to transfer and fix the toner image from the intermediate transfer belt 5 to the sheet 8. It has a transfer fixing process. Here, the preliminary transfer process is a process of applying an electrostatic force to the toner image. The details will be described below.

The surfaces of the photosensitive drums 1Y, 1M, 1C, 1K corresponding to the respective colors rotating in the direction of arrow A shown in FIG. 1 are uniformly charged by the chargers 2Y, 2M, 2C, 2K. Next, in response to the toner image forming signals of the respective colors, the surfaces of the photosensitive drums 1Y, 1M, 1C, 1K corresponding to the respective colors are scanned with spot lights 3Y, 3M, 3C, 3K to form electrostatic latent images of the respective colors. I do. Next, the developing units 4Y, 4M, 4C, 4K
To develop with the toner of each color, and the respective photosensitive drums 1Y,
A toner image of each color is formed on 1M, 1C, and 1K. The intermediate transfer belt 5 includes a heating roll 11 and a plurality of roll members 7.
And rotates in the direction of arrow B at the same speed as the photosensitive drums 1Y, 1M, 1C, and 1K.
The toner images of the respective colors formed on 1M, 1C, and 1K are sequentially transferred onto the intermediate transfer belt 5 by primary transfer means 6 (bias transfer rolls). At this time, it is important to adjust the timing so that the toner images of the respective colors are accurately overlapped on the intermediate transfer belt 5.

The intermediate transfer belt 5 on which the multicolor toner image is formed is superimposed on the sheet 8 conveyed by the sheet conveying means 9. Further, when the leading portion of the sheet 8 reaches the corotron 10 serving as the preliminary transfer unit, corona discharge is started, and a positive charge is applied to the back surface of the sheet 8. As a result, the toner sandwiched between the intermediate transfer belt 5 and the paper 8 has
An electrostatic attraction force acts in the direction of the sheet 8, and FIG.
As shown in (2), the toner of the portion of the toner image formed on the intermediate transfer belt 5 that is not in contact with the paper 8 moves to the paper 8.

When the leading end of the paper 8 reaches the heating roll 11, the intermediate transfer belt 5 is heated by the heating roll 11, and is further pressed by the pressing roll 12 via the paper 8. As a result, the toner packed in the intermediate transfer belt 5 and the paper 8 is heated and melted and thermally transferred to the paper 8. In this way, Corotron 1
0, the toner preliminarily transferred is heated and melted and fixed on the sheet 8.

FIG. 2 is a diagram schematically showing the state of preliminary transfer in the image forming apparatus shown in FIG.

In Step 1 shown in FIG. 2, the toner image 10
The intermediate transfer belt 5 on which 1 is formed and the sheet 8 are in a state before being superposed. In step 2, the intermediate transfer belt 5 and the sheet 8 are superimposed. In this state, as shown in the area A, the toner image 101 is sandwiched between the intermediate transfer belt 5 and the paper 8 and packed, but due to the surface roughness of the paper 8, the toner image 101 There is a portion where the image 101 and the sheet 8 are not in close contact. The toner in this portion is preliminarily transferred to the sheet 8 as shown in step 3. Further, the intermediate transfer belt 5 and the sheet 8 are heated and pressurized while being superposed, and the toner in the area A packed between the intermediate transfer belt 5 and the sheet 8 is thermally transferred and fixed to the sheet 8 simultaneously. Is done. Since the toner in the area B in the unpacked area has been moved to the sheet 8 in advance, it is heated and fixed on the sheet 8 as it is. Finally, in step 4, the intermediate transfer belt 5 and the sheet 8 are separated, and the toner image 101 formed on the intermediate transfer belt 5 is transferred and fixed to the sheet 8 without causing transfer omission.

Accordingly, even if a thick elastic layer is formed on the surface of the intermediate transfer belt 5 or a high load is not applied to the thermal transfer fixing section, the occurrence of transfer failure due to the surface roughness of the paper 8 can be prevented. . Thereby, high-speed suitability and reduction of heat energy can be realized by thinning the belt, and shortening of warm-up time can be realized by thinning the heating means. Further, since it is not necessary to apply a large load to the thermal transfer fixing unit, the thermal transfer fixing unit can be realized with a simple support mechanism, thereby preventing an increase in the size, weight, and cost of the apparatus.

As described above, in this embodiment, thermal transfer fixing is performed after the toner which is not in close contact with the paper 8 is moved from the intermediate transfer belt 5 to the paper 8 in advance by the corotron 10 (preliminary transfer means). As described with reference to FIG. 2, even if there is a poor adhesion between the toner image 101 and the paper 8 due to the surface roughness of the paper 8, the toner in that portion is transferred to the paper 8 in advance. In addition, even when the paper 8 having a rough surface is used, transfer omission is prevented from occurring. Further, as described above, since the preliminary transfer is performed in a state where the intermediate transfer belt 5 and the sheet 8 are always overlapped, the toner image is hardly disturbed by the preliminary transfer. Further, in the thermal transfer fixing section, since the image is non-electrostatically transferred by the physical adhesive force, the transfer and fixing with less unevenness and disturbance can be performed irrespective of the layer thickness of the toner and the electrical properties of the paper.

Thereafter, the intermediate transfer belt 5 and the paper 8 pressed by the pressure roll 12 are conveyed in a state of being in close contact with each other, and reach the roll member 7 having a small curvature.
Is the intermediate transfer belt 5 depending on the strength of the paper 8 itself.
Peeled off from If the toner image sandwiched between the intermediate transfer belt 5 and the sheet 8 is not sufficiently cooled before reaching the part to be separated, the cohesive force Ft of the toner image becomes Ft>
Since the force relationship of Fr (Fr: adhesion force between the toner and the intermediate transfer belt 5) is not achieved, in the present embodiment, the cooling unit 15 is disposed, and the toner image is cooled until the relationship of the force is established. As the cooling means 15, a simple air cooling fan or the like is used.

In the image forming apparatus 100 of this embodiment, even if a high-resolution digital image is formed using a paper having a rough surface (the above-described plain paper or recycled paper), a low density portion, a fine line, According to the conventional technique, a portion where transfer omission is remarkable, such as fine character details, is well transferred, and a very high quality image can be formed with almost no density unevenness.

The intermediate transfer belt 5 used in the present embodiment has a small thickness of 35 μm in total and has a small heat capacity. Therefore, the energy required for heating the toner via the intermediate transfer belt 5 by the heating roll 11 is sufficient. Is small. In the present embodiment, it is possible to thermally transfer and fix 30 or more A4-size paper images per minute by the heating roll 11 having the built-in heat source having the rated power of 650 W.

In the conventional image forming apparatus 500 shown in FIG. 10, when the thin-film intermediate transfer belt 5 used in the present embodiment is used and thermal transfer fixing is performed under the same pressure as in the present embodiment, the front surface is fixed. When a rough paper was used, transfer omission occurred remarkably due to insufficient adhesion between the toner and the paper, and an acceptable image quality was not obtained. When an elastic layer is formed on the surface of the intermediate transfer belt 5 and an image quality equivalent to the image formed in the present embodiment is to be realized, an elastic layer of silicon rubber or the like is formed on the base layer by 50 μm to 100 μm. Must be formed, and the energy consumption is more than doubled.

In this embodiment, since the thickness of the intermediate transfer belt 5 is small as described above, heat is quickly transmitted from the heating roll 11 to the toner via the intermediate transfer belt 5. Therefore, the heating time of the toner is short, and the intermediate transfer belt 5
It is not necessary to lengthen the contact portion between the heating roll 11 and the heating roll 11, and a small-diameter heating roll 11 can be used. In the present embodiment, 30 or more A4-size images can be thermally transferred and fixed per minute by using the heating roll 11 having a diameter of 30 mm as described above.

When an intermediate transfer belt having a 50 μm silicon elastic layer formed on its surface is used by using the same heating roll as in this embodiment, heat conduction to the toner is poor, and the toner is sufficiently heated in a short time. Therefore, only about 10 A4 size images can be thermally transferred and fixed per minute. To increase the speed, it is necessary to increase the temperature of the heating roll or increase the diameter of the heating roll,
There is a problem that energy consumption is increased and the size of the device is increased.

Further, in the conventional image forming apparatus 500, the pressure of the thermal transfer fixing section is increased by using the thin-film intermediate transfer belt 5 used in this embodiment, and the same as the image formed in this embodiment. In order to realize image quality, the nip pressure is required to exceed 10 kg / cm ² , and the stress on the intermediate transfer belt 5 and the paper 8 becomes too strong, causing wrinkles on the paper 8 and the intermediate transfer belt 5. The problem arises that is damaged. Further, in order to withstand a high nip pressure, the thickness of the heating roll must be increased to several mm or more, which causes a problem that the heat capacity of the heating roll increases and the warm-up time becomes extremely long. further,
There is also a problem that a mechanism for supporting a high nip load becomes complicated, and the device becomes large in size and high in cost.

In the present embodiment, a corotron, which applies an electrostatic force to a toner image, is used as a pre-transfer unit that applies a force in the direction in which the toner image is transferred from the intermediate transfer belt 5 to the sheet 8. Although described above, the present invention is not limited to this, and the pre-transfer unit of the present invention may be one using physical adhesion such as pressure transfer or adhesive transfer, or one using magnetic force. Among them, particularly, those using electrostatic force can use the chargeability of the toner itself as it is, and can transfer the toner image to the paper using a simple electrostatic transfer unit used as a conventional toner image transfer unit. .

When the electrostatic transfer is adopted as the preliminary transfer, the toner is electrostatically moved in a state where the intermediate transfer belt 5 and the sheet 8 are overlapped, and then the intermediate transfer belt 5 and the sheet 8 are separated. And has the advantage of being transported to the thermal transfer fixing unit.

FIG. 3 is a diagram for explaining disturbance of a toner image in an image forming apparatus as a comparative example.

A conventional image forming apparatus 600 as a comparative example shown in FIG. 3 has a charger 2 for uniformly charging the toner image carrier 31 (photosensitive drum), and a toner 2 by irradiating exposure light 3 to the toner. Image exposure apparatus for forming an electrostatic latent image on image carrier 31
(Not shown) and a developing device 4 for developing the electrostatic latent image formed on the toner image carrier 31 with toner to form a toner image
, A cleaning unit 13 and a bias transfer roll 6.

In the conventional image forming apparatus 600, when the toner image carrier 31 is electrostatically transferred from the toner image carrier 31 to the sheet 8, the toner image carrier 31 Transfer unevenness occurs at a transfer portion, which is a portion facing the bias transfer roll 6 and the bias transfer roll 6. In addition to this, the toner image is scattered due to gap transfer occurring immediately before the transfer portion shown in FIG. Disturbance of the toner image due to peeling discharge generated at the peeling portion between the toner image carrier 31 and the sheet 8 shown in the middle D is a major problem.

On the other hand, since the electrostatic pre-transfer in the present embodiment is performed in a state where the intermediate transfer belt 5 and the paper 8 are superimposed as described above, there is no gap immediately before the transfer section, and The intermediate transfer belt 5 and the sheet 8 are separated after heating. Therefore, the above-described disturbance of the toner image before and after the electrostatic preliminary transfer is prevented. In the transfer section, only the toner that is not packed in the intermediate transfer belt 5 and the paper 8 is electrostatically moved, and while moving through a very small gap, slight disturbance occurs, but the image quality due to the disturbance is reduced. Deterioration is very small. Therefore, the toner that is not in contact with the paper 8 can be moved to the paper 8 by the electrostatic pre-transfer with almost no deterioration of the electrostatic image quality.

Further, according to the image forming apparatus 100 of the present embodiment, even if the intermediate transfer belt 5 having a small thickness is used and a high load is not applied to the thermal transfer fixing section, the conventional transfer simultaneous fixing can be performed. The transfer failure caused by the surface roughness of the sheet, which has been a problem in the image forming apparatus of the system, can be prevented from occurring, and a high-quality image can be formed on various kinds of sheets.

Further, by making the intermediate transfer belt 5 thinner, the speed and heat energy can be reduced, and the warm-up time can be shortened by making the heating means thinner. Moreover, since it is not necessary to apply a large load to the thermal transfer fixing section, the apparatus can be realized with a simple supporting mechanism, and the apparatus can be prevented from increasing in size, weight, and cost.

Further, by using the simple electrostatic transfer means used as the conventional toner image transfer means, the toner which is not in contact with the sheet is hardly disturbed at the time of preliminary transfer. It can be moved to the paper.

FIG. 4 is a schematic configuration diagram of a second embodiment of the image forming apparatus of the present invention.

The same components as those of the image forming apparatus 100 shown in FIG. 1 will be described with the same reference numerals.

The image forming apparatus 200 shown in FIG. 4 includes a photosensitive drum 1 rotating in the direction of arrow A, a charger 2 for uniformly charging the surface of the photosensitive drum 1 to a desired potential, and a photosensitive member. An image exposure device (not shown) that scans the surface of the drum 1 with a spot light 3 according to an image signal to form an electrostatic latent image on the photosensitive drum 1, and a photosensitive drum 1 on which the electrostatic latent image is formed
Are developed using color toners of yellow, magenta, cyan, and black, respectively.

The image forming apparatus 200 includes an intermediate transfer belt 5 on which the toner image formed on the photosensitive drum 1 is primarily transferred, and a toner image on the photosensitive drum 1 on the intermediate transfer belt 5. A primary transfer means 6 for performing electrostatic transfer so as to be superposed on each other and a roll member 7 for bridging the intermediate transfer belt 5 are provided.

Further, the image forming apparatus 200 includes a sheet conveying means 9 for conveying the intermediate transfer belt 5 on which the toner image is formed and the sheet 8 in a superposed manner, and a toner image formed on the intermediate transfer belt 5. , A roll-shaped electrode member 16 for electrostatically moving the intermediate transfer belt 5, a heating roll 11 for heating the toner image from the back surface of the intermediate transfer belt 5, Paper 8
And a pressure roll 12 for applying pressure to the pressure roller.

Further, after the toner image is transferred to the intermediate transfer belt 5, the photosensitive drum 1
Cleaning means 1 for cleaning the residual toner on the surface
3, a belt cleaning unit 14 for removing toner, paper dust, and the like remaining on the intermediate transfer belt 5 after transferring the toner image onto the paper 8; And cooling means 15 for cooling paper 8
And are provided.

Here, the intermediate transfer belt 5 in this embodiment corresponds to the toner image carrier of the present invention, and forms a toner image on the photosensitive drum 1 and transfers it to the intermediate transfer belt 5. The above steps correspond to the toner image forming means of the present invention. Further, the roll-shaped electrode member 16 corresponds to a preliminary transfer unit in the present invention.

The intermediate transfer belt 5 in this embodiment is
The same one as the image forming apparatus 100 of the first embodiment is used, and is stretched around the heating roll 11 and the plurality of roll members 7.
The photosensitive drum 1 is contacted with a certain width,
The photosensitive drum 1 rotates in the direction of arrow B at the same speed.

As the primary transfer means 6 of this embodiment, a corotron which applies a high voltage to the electrode wires and generates corona discharge is used. A voltage of 4 kV to 7 kV is applied thereto, and a positive charge having a polarity opposite to that of the toner is applied from the back surface of the intermediate transfer belt 5, and the toner image on the photosensitive drum 1 is transferred to the intermediate transfer belt 5. The primary transfer of the present embodiment is also a transfer of the toner image from the photosensitive drum 1 to the intermediate transfer belt 5, and since the surface shape and the electrical characteristics of both can be controlled as described above, unevenness and disturbance Less electrostatic transfer can be performed.

As the pre-transfer means in this embodiment, a roll-shaped electrode member 16 coated with silicone rubber foamed on a hollow metal roll is used. Ion conductor is compounded in silicone rubber, and electric resistance is 10 ⁶
Ω · cm to 10 ⁸ Ω · cm. There are several methods for arranging the roll-shaped electrode members 16. In the present embodiment, as shown in FIG. 4, the intermediate transfer belt 5 and the paper 8 are used by using two roll-shaped electrode members 16. Are arranged so as to sandwich them. A voltage of 1 kV to 2 kV is applied between the two roll-shaped electrode members 16 so as to form an electric field for moving the toner to the paper 8 side. The two roll-shaped electrode members 16 are about 9.8 N to 98 N (1 kgf).
A roll electrode member 16
Is so-called co-rotation, which is accompanied by the intermediate transfer belt 5.

FIG. 5 is a diagram showing a peripheral portion of the pre-transfer device different from the pre-transfer device in the image forming apparatus shown in FIG.

The image forming apparatus 200 shown in FIG. 4 has been described by way of an example having two roll-shaped electrode members 16. However, as shown in FIG.
About 9.8 N to 98 N (1 kg)
f to 10 kgf). By doing so, the roll-shaped electrode member 16 has -1.
A voltage of kV to -2 kV is applied to the intermediate transfer belt 5.
A negative charge having the same polarity as that of the toner is applied to the back surface, and the toner can be moved toward the paper 8 by a repulsive force against the charge.
Alternatively, the roll-shaped electrode member 16 may be disposed on the paper 8 side, and a positive charge having a polarity opposite to that of the toner may be applied to the back surface of the paper 8.

The description will be continued with reference to FIG. The sheet conveying unit 9 in the image forming apparatus 200 of the present embodiment,
The roll-shaped electrode member 16 and the pressure roll 12 are configured such that the pressure mechanism can be retracted, and are retracted to the retract position while the toner image of each color is formed on the intermediate transfer belt 5. It is separated from the intermediate transfer belt 5. At the timing when the formation of the multicolor toner image on the intermediate transfer belt 5 is completed and the sheet 8 is conveyed to the above-described respective member positions, the respective members are set at the positions where they are pressed against the intermediate transfer belt 5. Is done. Similarly, the belt cleaning means 14 is configured such that the pressure mechanism can be retracted, and after the multicolor toner image formed on the intermediate transfer belt 5 is transferred to the paper 8, the intermediate transfer belt 5
It is set at the position where it is pressed against.

According to the image forming method of the image forming apparatus 200 of this embodiment, first, the surface of the photosensitive drum 1 that is driven to rotate in the direction of arrow A is uniformly charged by the charger 2. Next, the surface of the photosensitive drum 1 is scanned with the spot light 3 according to the image signal of the first color (for example, black), and an electrostatic latent image is formed. Next, the toner is developed with black toner by the developing device 4K, and a black toner image is formed on the photosensitive drum 1. The first color toner image formed on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 5 by the primary transfer member 6, and unnecessary toner on the photosensitive drum 1 that has not been transferred is removed by the cleaning unit 13. Is scraped off. The photosensitive drum 1 further rotates, and the second color (for example, cyan) image forming cycle starts at the timing when the toner image formation start point on the photosensitive drum 1 returns to the position facing the charger 2 again. Is done. The circumferential length of the intermediate transfer belt 5 is an integral multiple of the outer circumference of the photosensitive drum 1, particularly, is equal to one in the present embodiment, and the toner image formed on the photosensitive drum 1 is transferred by the primary transfer member 6. The images are sequentially superimposed and transferred. In this way, the multicolor toner images are formed on the intermediate transfer belt 5 by superimposing the toner images of the respective colors.

The intermediate transfer belt 5 on which the multicolor toner image is formed is superimposed on the sheet 8 conveyed by the sheet conveying means 9. When the leading portion of the paper 8 reaches the roll-shaped electrode member 16 serving as the preliminary transfer means, the roll-shaped electrode member 1
A voltage is applied to the sheet 6 so as to move the toner image toward the sheet 8. As a result, an electrostatic suction force acts on the toner sandwiched between the intermediate transfer belt 5 and the paper 8 in the paper 8 direction,
The portion of the toner image formed on the intermediate transfer belt 5 that is not in contact with the sheet 8 as shown in FIG.
The toner in the area B) moves to the sheet 8.

Further, according to the roll-shaped electrode member 16 used in the present embodiment, the electric field is applied while the intermediate transfer belt 5 and the paper 8 are being pressed, so that the toner is moved in a state where both are more closely contacted. Thus, preliminary transfer with less disturbance can be performed.

After that, since the steps after the thermal transfer fixing step are the same as those in the first embodiment, the description is omitted.

According to the image forming apparatus 200 of the present embodiment, similarly to the image forming apparatus 100 of the first embodiment, there is almost no density unevenness, and even when a high-resolution digital image is formed, there is almost no transfer omission. High-quality images can be stably formed on various sheets having different surface shapes.

Further, since it is not necessary to form an elastic layer or the like on the toner image carrier (intermediate transfer belt 5), high-speed suitability by reducing the thickness of the belt and reduction of thermal energy are realized. Further, since it is not necessary to apply a large load to the thermal transfer fixing unit, the warm-up time can be shortened by reducing the thickness of the heating unit. Further, the thermal transfer fixing section is realized by a simple supporting mechanism, and it is possible to prevent an increase in the size, weight, and cost of the apparatus.

FIG. 6 is a schematic configuration diagram of a third embodiment of the image forming apparatus of the present invention.

The same components as those of the image forming apparatus 100 shown in FIG.

The image forming apparatus 300 shown in FIG. 6 includes a dielectric belt 17 rotating in the direction of arrow B and a dielectric belt 1.
An ion flow recording head 18 for forming an electrostatic latent image by applying a charge to the surface of the recording medium 7 in accordance with an image signal and a dielectric belt 17 on which the electrostatic latent image is formed are separated into yellow, magenta, cyan and black colors. Each color developing device 4Y for developing using toner,
4M, 4C, and 4K, and a roll member 7 for stretching the dielectric belt 17 are provided.

Further, the image forming apparatus 300 includes a sheet conveying unit 9 for conveying the dielectric belt 17 on which the multicolor toner image is formed and the sheet 8 in a superposed manner, and a sheet 8 superposed on the dielectric belt 17. A corotron 10 that emits a corona charge from the back surface thereof, and a vibration providing unit 19 that is in contact with the back surface of the dielectric belt 17 facing the corotron 10 and vibrates the dielectric belt 17 and the sheet 8 are provided.
The vibration applying means 19 applies a peeling force due to vibration to the toner image on the dielectric belt 17 in addition to the electrostatic force, so that the toner can be easily moved to the paper 8 and the preliminary transfer can be performed more reliably. . In addition, the dielectric belt 17 and the sheet 8 are in a state of being superposed, and unnecessary disturbance of the toner image due to vibration hardly occurs.

Further, the image forming apparatus 300 includes a heating roll 11 for heating the multicolor toner image from the back surface of the dielectric belt 17,
And a pressure roller 12 for applying pressure to the paper 8, and a belt cleaning unit 14 for removing toner, paper dust, and the like remaining on the dielectric belt 17 after transferring the toner image onto the paper 8.
And are provided. Further, if necessary, a cooling unit 15 for cooling the heated and pressurized dielectric belt 17 and the paper 8 is provided.

Incidentally, the dielectric belt 17 corresponds to the toner image carrier of the present invention, and the developing units 4Y, 4M, 4
C and 4K correspond to the toner image forming means of the present invention. Further, the corotron 10 and the vibration providing unit 19 correspond to a preliminary transfer unit in the present invention.

As the dielectric belt 17, a conductive belt such as SUS or aluminum coated with a thermoplastic resin having a high insulating property, or a belt obtained by molding a resin having a high insulating property as it is, may be used. it can. However,
A metal belt based on a metal belt such as SUS or aluminum has a large specific heat of metal, so that even if the belt has the same thickness, the heat capacity of the belt becomes large and energy consumption increases. Therefore, in this embodiment, a polyimide resin molded in a belt shape by a centrifugal molding method is used. The thickness is 30 μm.

As in the first and second embodiments, the polyimide belt is coated with a 5 μm-thick silicon copolymer as a surface layer. Silicon copolymer is
As described above, it has the property of easily separating from the toner that has been melted and fluidized by heat, and has sufficiently high insulation properties, so that it is suitable as a surface layer of the dielectric belt 17.

FIG. 7 is a schematic configuration diagram of an ion flow recording head in the image forming apparatus shown in FIG.

An ion flow recording head 18 shown in FIG.
Comprises an air ion generator 20 and an ion flow controller 21. As shown in FIG. 7, the air ion generator 20 generates air ions by applying a high voltage to the electrode wires and causing corona discharge between the electrode wires and the shield member. Further, the ion flow control unit 21 has a control electrode divided into a desired resolution in the recording width direction and an opening for irradiating the surface of the dielectric belt 17 with ions generated by the aerial ion generation unit 20. The passing of the generated ions through the opening is controlled by the polarity of the voltage applied to the control electrode. The ion flow control unit 21 is disposed so as to face the dielectric belt 17, and ions passing through the opening adhere to the dielectric belt 17 according to an electric field formed between the control electrode and the dielectric belt 17. I do. A voltage is applied to each control electrode according to an image signal, and an electrostatic latent image is formed on the dielectric belt 17.

Incidentally, since the dielectric belt 17 used in this embodiment does not include a conductive layer, the electrode member 22 is disposed at a position facing the ion flow recording head 18.
Thereby, an electrostatic latent image is formed stably. Similarly, electrode members 22Y, 22M, 22C, and 22K are arranged at positions facing the developing devices 4Y, 4M, 4C, and 4K, respectively.
Thereby, development is stably performed. In the present embodiment, the electrode members 22, 22Y, 22M, 22C, 22K are used.
Is grounded.

The vibration providing means 19 used in the present embodiment uses a ceramic-based piezoelectric element attached to the back surface of a SUS plate, and drives the piezoelectric element at a high frequency to resonate the SUS plate. Let it. Here, the piezoelectric element having a resonance frequency of 40 kHz exceeding an audible range is used in consideration of noise. Also, SUS
The plate is brought into contact with the dielectric belt 17 with a load of about 9.8 N (1 kgf) to vibrate the dielectric belt 17.
Furthermore, the edge of the SUS plate that contacts the dielectric belt 17 is rounded, so that the wear of the dielectric belt 17 is minimized. It should be noted that the vibration providing means 19 is not limited to this, and any other means for providing vibration to the dielectric belt 17 may be used.

Next, an image forming method according to the present embodiment will be described. First, an electrostatic latent image is formed on the surface of the dielectric belt 17 circulating in the direction of the arrow B in accordance with an image signal of the first color (for example, black) by the ion flow recording head 18, and the black toner is formed by the developing device 4 </ b> K. And a black toner image is formed on the dielectric belt 17. Then
The dielectric belt 17 on which the black toner image is formed circulates in the direction of arrow B, and coincides with the timing at which the toner image formation start point of the dielectric belt 17 returns to the position facing the ion flow recording head 18 again. The image forming cycle for the second color (for example, cyan) is started.

After the black, yellow, magenta, and cyan toner images are superimposed on the dielectric belt 17 to form a multicolor toner image, the dielectric belt 17 further circulates, and the paper conveying means 9 Is superimposed on the sheet 8 conveyed. When the leading portion of the sheet 8 reaches the corotron 10 serving as the preliminary transfer unit, corona discharge is started, and a positive charge is applied to the back of the sheet 6. At the same time, the dielectric belt 17 is vibrated by the vibration providing means 19. As a result, an electrostatic attraction force in the paper direction and a peeling force due to vibration act on the toner sandwiched between the dielectric belt 17 and the paper 8, and a toner image formed on the dielectric belt 17 is formed. The portion of the toner that is not in contact with the sheet 8 moves to the sheet 8 quickly. In addition, Corotron 10
Are the same as those used in the first embodiment, and the applied voltage has the same value.

According to the image forming apparatus 300 of the present embodiment, similarly to the first and second embodiments, there is almost no density unevenness, and even if a high-resolution digital image is formed, high image quality with almost no transfer omission is obtained. An image can be stably formed on various sheets having different surface shapes.

Further, the toner image carrier (the dielectric belt 1)
Since it is not necessary to form an elastic layer or the like in 7), high-speed suitability by reducing the thickness of the belt and reduction of thermal energy are realized. Also, since it is not necessary to apply a large load to the thermal transfer fixing unit, the warm-up time can be shortened by reducing the thickness of the heating unit. Further, the thermal transfer fixing section is realized by a simple supporting mechanism, and it is possible to prevent an increase in the size, weight, and cost of the apparatus.

Further, the pre-transfer can be performed more efficiently than the electrostatic pre-transfer described in the first and second embodiments, and an image without transfer omission can be formed.

FIG. 8 is a diagram showing the peripheral portion of the pre-transfer means in the fourth embodiment of the image forming apparatus of the present invention.

Note that the same components as those of the image forming apparatus 100 shown in FIG.

In the present embodiment, before the toner image formed on the intermediate transfer belt 5 and the sheet 8 are superimposed, the electric charge for giving the electric charge of the same polarity as the toner to the intermediate transfer belt 5 on which the toner image is formed is provided. An application unit 23 is provided. The roll-shaped electrode member 16 described in the second embodiment is used as the preliminary transfer unit.

As the charge applying means 23, a corotron is used in the present embodiment. Since the corotron can apply the electric charge without contact, the electric charge is applied without disturbing the toner image. A voltage of −5 kV to −6 kV is applied to the wire electrode of the corotron, and a negative charge having the same polarity as the toner is applied to the intermediate transfer belt 5 on which the toner image is formed.

According to the image forming apparatus 400 of this embodiment, a charge having a polarity which assists the preliminary transfer by the roll-shaped electrode member 16 is applied to the toner image carried on the intermediate transfer belt 5 before the paper 8 is superimposed. Charge applying means 23 for applying
Is provided, the charge amount of the toner held on the intermediate transfer belt 5 increases, and the intermediate transfer belt 5 is charged to the same polarity as the toner. Therefore, when an electric field for attracting the toner toward the paper 8 is applied by the roll-shaped electrode member 16, the toner receives a larger electrostatic attraction force, and the electrostatic repulsion between the toner and the intermediate transfer belt 5 occurs. Since the force acts, the toner can be easily moved to the sheet 8, and the preliminary transfer can be performed more reliably. Further, when the sheets 8 are superimposed, the adhesion between the intermediate transfer belt 5 and the sheet 8 is improved by the electrostatic attraction force, so that preliminary transfer with less disturbance can be performed. Therefore, the pre-transfer can be performed more efficiently than the electrostatic pre-transfer described in the first and second embodiments, and an image without transfer omission can be formed.

Here, in each of the above-described embodiments, the surface shape measuring means for measuring the surface shape of the sheet 8 before the image is formed on the sheet tray or the sheet conveying path, and the measurement result by the surface shape measuring means. Pre-transfer control means for controlling whether or not to activate the pre-transfer means based on

FIG. 9 is a schematic configuration diagram of the surface shape measuring means.

The surface shape measuring means 24 shown in FIG. 9 has an LED lamp 25 for irradiating the surface of the sheet 8 with light for measurement.
And a two-dimensional CCD sensor 27 for taking in reflected light from the surface of the paper 8 via a lens 26. The surface shape measuring means 24 measures the surface shape of the sheet 8 from the output data of the CCD sensor 27.

The two-dimensional data taken in from the CCD sensor 27 is limited in spatial frequency band by a band-pass filter (not shown), and the surface roughness of the sheet 8 is calculated from the two-dimensional data in which the spatial frequency band is limited. . The calculated data of the surface roughness of the sheet 8 is input to a pre-transfer control means (not shown) for controlling the pre-transfer, and based on the surface roughness data, whether or not the pre-transfer control means performs pre-transfer. Is determined.

When the paper 8 having a smooth surface is used, the adhesion between the toner image and the paper 8 is good, so that good thermal transfer fixing can be performed without performing preliminary transfer. Therefore, in the present embodiment, the surface shape of the sheet 8 is measured by the surface shape measuring unit 24, and the preliminary transfer is performed by the preliminary transfer control unit based on the measurement result, that is, only when the paper 8 having a rough surface is used. In this way, unnecessary energy consumption due to the preliminary transfer can be reduced. still,
For the measurement of the surface shape of the sheet 8, various known displacement meters such as a stylus type shape measuring device and a laser displacement meter can be used.

The types of paper 8 include smooth paper having a smooth surface,
It is set in two stages with plain paper having a rough surface. here,
The ten-point average roughness is used among several indices of the surface roughness. When the value of the ten-point average roughness is 10 μm or less, it is determined that the paper is smooth. Needless to say, the reference value for the above determination can be changed depending on the toner used, the toner image carrier, and the configuration and conditions of the thermal transfer fixing unit. Further, the type of the paper 8 may be determined based on the center surface roughness or the area average roughness which is another index of the surface roughness.

According to the configuration and conditions of the various members and the thermal transfer fixing section used in each embodiment, when smooth paper having a ten-point average roughness value of 10 μm or less is used, even if preliminary transfer is not performed. Although a high-quality image without transfer omission can be formed, transfer omission starts to occur without pre-transfer when a paper having a higher roughness is used.

Thus, the sheet 8 before the image is recorded
When using smooth paper that does not require pre-transfer, it is provided with surface shape measuring means 24 for measuring the surface shape of the paper 8 and automatically determining whether or not to perform pre-transfer according to the type of paper 8. By not performing the preliminary transfer, unnecessary energy consumption due to the preliminary transfer can be reduced. In addition, whether or not to perform the preliminary transfer may be manually switched without providing the surface shape measuring means 24.

The present invention is not limited to the above-described embodiments, but includes various modifications having the same purpose.
It includes combinations. Also, the toner image forming means has been described as an electrostatic recording type, but is not limited to this. For example, a toner is formed on a predetermined toner image carrier based on digitally processed image data. A method in which a toner image is formed by direct flight may be used, or a magnetic latent image is formed on a predetermined toner image carrier based on digitally processed image data, and based on the magnetic latent image. A method of forming a toner image may be used.

[0134]

As described above, according to the image forming method of the present invention, even if a high-resolution digital image is formed on a recording medium having a rough surface, even if a low-density portion, a fine line, or a fine character of a monochromatic image is formed. Parts such as details, in which transfer omission has been noticeable due to insufficient adhesion between the toner and the recording medium in the conventional method, can be moved to the recording medium in advance by preliminary transfer, so that the toner image can be reliably transferred to the paper. it can.

Further, according to the image forming apparatus of the present invention, a high-quality image having almost no density unevenness and almost no transfer omission even when a high-resolution digital image is formed can be transferred to various recording media having different surface shapes. Can be formed stably.

Further, since it is not necessary to form an elastic layer or the like on the toner image carrier, high speed suitability by thinning the belt,
In addition, reduction of heat energy is realized. Further, since it is not necessary to apply a large load to the thermal transfer fixing unit, the warm-up time can be reduced by reducing the thickness of the heating unit. Further, the thermal transfer fixing section is realized by a simple supporting mechanism, and it is possible to prevent an increase in the size, weight, and cost of the apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of an image forming apparatus of the present invention.

FIG. 2 is a view schematically showing a state of preliminary transfer in the image forming apparatus shown in FIG.

FIG. 3 is a diagram for explaining disturbance of a toner image in an image forming apparatus as a comparative example.

FIG. 4 is a schematic configuration diagram of a second embodiment of the image forming apparatus of the present invention.

FIG. 5 is a diagram showing a peripheral portion of a pre-transfer unit different from the pre-transfer unit in the image forming apparatus shown in FIG.

FIG. 6 is a schematic configuration diagram of a third embodiment of the image forming apparatus of the present invention.

FIG. 7 is a schematic configuration diagram of an ion flow recording head in the image forming apparatus shown in FIG.

FIG. 8 is a diagram illustrating a peripheral portion of a pre-transfer unit in a fourth embodiment of the image forming apparatus of the present invention.

FIG. 9 is a schematic configuration diagram of a surface shape measuring unit.

FIG. 10 is a schematic configuration diagram of a conventional image forming apparatus employing a simultaneous transfer fixing method.

FIG. 11 is a diagram illustrating a transfer state of a toner image based on a magnitude relationship among the respective adhesive forces between the toner and the paper, the cohesive force between the toners, and the adhesive force between the toner and the toner image carrier.

FIG. 12 is a diagram schematically illustrating pixels of a high-resolution toner image formed on a toner image carrier, a surface shape of a sheet, and a state of thermal transfer fixing. FIG. 4 is a diagram schematically illustrating pixels of a high-resolution toner image formed on a toner image carrier, a surface shape of a sheet, and a state of thermal transfer fixing.

[Explanation of symbols]

1,1Y, 1M, 1C, 1K Photoconductor drum 2,2Y, 2M, 2C, 2K Charger 3,3Y, 3M, 3C, 3K Spot light 4,4Y, 4M, 4C, 4K Developing device 5 Intermediate transfer belt 6 Primary transfer means 7 Roll member 8 Paper 9 Paper transport means 10 Corotron 11 Heating roll 12 Pressure roll 13, 13Y, 13M, 13C, 13K Cleaning means 14 Belt cleaning means 15 Cooling means 16 Roll electrode member 17 Dielectric belt 18 Ion Flow recording head 19 Vibration providing means 20 Ion generating section 21 Ion flow controlling section 22, 22Y, 22M, 22C, 22K Electrode member 23 Charge applying means 24 Surface shape measuring means 25 LED lamp 26 Lens 27 CCD sensor 100, 200, 300, 400 Image forming apparatus 101 Toner image

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H032 AA05 AA14 AA15 BA09 BA21 BA25 BA27 2H033 AA21 AA30 AA32 BA29 BB06 BB29 BE09 2H078 AA18 AA29 BB12 CC06 DD03 DD29 DD42 DD53 DD57 DD73

Claims (7)

[Claims] An image forming method for forming a toner image on a recording medium by forming a toner image and finally transferring and fixing the formed toner image on a predetermined recording medium. A superimposing step of superposing a toner image carrier carrying a toner image and a recording medium so as to sandwich the toner image carried on the toner image carrier between the recording medium and the recording medium; A pre-transfer step of performing pre-transfer by applying a force to the toner image on the toner image carrier in a direction in which the toner image is transferred from the toner image carrier to the recording medium; Transferring the toner image from the toner image carrier to the recording medium by heating and pressurizing the toner image carrier and the recording medium in the superimposed state. An image forming method comprising: a fixing step. 2. The image forming method according to claim 1, wherein the preliminary transfer step is a step of applying an electrostatic force to the toner image. 3. An image forming apparatus that forms a toner image on a recording medium by forming a toner image and finally transferring and fixing the formed toner image on a predetermined recording medium. A predetermined toner image carrier, a toner image forming means for carrying a toner image on the toner image carrier, and a toner image carried on the toner image carrier interposed between the toner image carriers A recording medium conveying means for conveying the recording medium in an overlapping manner, and a state in which the recording medium is superimposed at a predetermined preliminary transfer position in the middle of being conveyed in a state where the toner image carrier and the recording medium are superimposed. A pre-transfer unit for applying a force to the toner image on the toner image carrier in the direction in which the toner image is transferred from the toner image carrier to the recording medium; and a recording medium by the recording medium conveying unit. The toner image carrier and the recording medium in a superimposed state are heated and further pressurized on the downstream side of the preliminary transfer position in the feeding direction, thereby transferring the toner image from the toner image carrier to the recording medium. And an image forming apparatus comprising: a transfer fixing unit for performing fixing. 4. An image forming apparatus according to claim 3, wherein said pre-transfer means applies an electrostatic force to the toner image. 5. The image forming apparatus according to claim 3, further comprising a vibration applying unit that vibrates the toner image carrier and the recording medium during the preliminary transfer by the preliminary transfer unit. 6. A method according to claim 1, further comprising the step of: applying a charge having a polarity which assists the preliminary transfer by the preliminary transfer unit to the toner image carried on the toner image carrier before the recording medium is superimposed. The image forming apparatus according to claim 4, wherein 7. A surface shape measuring means for measuring a surface shape of a recording medium before an image is recorded, and whether or not the preliminary transfer means is operated based on a measurement result by the surface shape measuring means. 4. The image forming apparatus according to claim 3, further comprising a preliminary transfer control unit.