KR20070023437A - Transparent toner and electrophotographic image forming apparatus using the same - Google Patents

Abstract

The disclosed electrophotographic image forming apparatus includes a printing unit which forms a toner image of at least one color on a recording medium by an electrophotographic method and coats transparent toner thereon, and a fixing unit for fixing the toner image and the transparent toner by applying heat and pressure thereto. It includes. The surface roughness of the roller in contact with the transparent toner of the fixing unit is Rz 15 µm or less.

Description

Transparent toner and electrophotographic image forming apparatus using the same

1 is a block diagram of an embodiment of an electrophotographic image forming apparatus according to the present invention;

2 is a block diagram of another embodiment of an electrophotographic image forming apparatus according to the present invention;

<Description of Symbols for Main Parts of Drawings>

1 ...... Image receptor 2 ...... Charge

3 ...... Exposure 4 ...... Developer

5 ...... Transfer belt 6 ...... 1 transfer machine

7 ...... Second transfer machine 8 ...... Fixing machine

10, 10a ... printing unit

The present invention relates to a toner and an electrophotographic image forming apparatus, and more particularly, to a transparent toner covering a color toner image and an electrophotographic image forming apparatus employing the same.

To obtain a color image using an electrophotographic image forming apparatus, four toners of yellow, cyan, magenta, and black are required. The color image can be transferred by superimposing four colors of toner onto the recording medium and then fixing it to the recording medium by applying heat and pressure.

The thickness of the toner layer of the image printed in monochrome is about 6-7 탆 when a toner having a volume average particle size of about 8 탆 is used. In the case of a color image printed by superimposing four toners, the thickness of the toner layer of the printed image may be up to about 30 µm. Due to such a thick toner layer, the image quality of the printed image does not reach the image quality of the thin offset printing. When the volume average particle size of the toner is about 6 mu m or less, the thickness of the toner layer can be made thin, but also does not fall short of the image quality of offset printing.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide an improved toner and an image forming method which can compensate for the deterioration of image quality due to a thick toner layer.

The transparent toner of the electrophotographic image forming apparatus of the present invention for achieving the above object is a transparent toner for an electrophotographic image forming apparatus which is superimposed and fixed together on a toner image forming a print image, and includes a base resin and a wax. And a charge control agent, wherein the wax content is higher than the wax content of the toner that forms the print image.

When the thickness of the transparent toner is fixed to 10 mu m, the average transmittance of the visible region is 40% or more.

The average particle diameter of the said wax particle is 4 micrometers or less.

The absolute value of the difference between the refractive index of the base resin and the refractive orange of the wax is 0.2 or less.

An electrophotographic image forming apparatus of the present invention for achieving the above object includes a printing unit for forming a toner image of at least one color on a recording medium by an electrophotographic method, and coating a transparent toner thereon; And a fixing unit for fixing the transparent toner by applying heat and pressure thereto, wherein the surface roughness of the roller in contact with the transparent toner of the fixing unit is Rz 15 µm or less.

The transparent toner has an average transmittance of 40% or more in the visible region when the thickness is 10 µm after fixing, the wax content is higher than the wax content of the toner forming the toner image, and the average particle size of the wax particles is 4 µm or less. .

The absolute value of the difference between the refractive index of the base resin of the transparent toner and the refractive orange of the wax is 0.2 or less.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram showing an embodiment of an electrophotographic image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 is a multi-pass type color image forming apparatus. Referring to Fig. 1, a printing unit 10 for transferring a toner image to a recording medium P in an electrophotographic method, and a fixing unit 8 for fixing the toner image to the recording medium P are disclosed. The printing unit 10 includes an image receptor 1, a charger 2, an exposure machine 3, a developer 4, a transfer belt 5, and a transfer roller 7. As the image receptor 1, a photosensitive member such as a photosensitive drum or a photosensitive belt, or an electrostatic drum (or an electrostatic belt) is used. In this embodiment, a photosensitive drum is used as the image receptor 1. The charger 2 charges the surface of the image receptor 1 to a uniform potential. In this embodiment, a charging roller to which a charging bias voltage is applied is used, but a corona discharger may be used. The exposure apparatus 3 is for forming an electrostatic latent image by scanning light corresponding to image information on the surface of the image receptor 1, and a laser scanning unit (LSU) using a laser diode as a light source is mainly used. When an electrostatic drum (or belt) is used as the image receptor 1, an electrostatic lock head is employed instead of the exposure machine 3. The developing device 4 supplies toner to the electrostatic latent image to develop the electrostatic latent image into a visible toner image. In order to form a color image, four developing apparatuses 4Y, 4C, 4M, and 4K containing toners of yellow, cyan, magenta, and black colors are required. The transfer belt 5 is an example of an intermediate transfer medium in which a toner image is temporarily transferred. A transfer drum (not shown) may be employed as the intermediate transfer medium. The first transfer bias 6 is applied to the first transfer machine 6 for transferring the toner image on the image receptor 1 to the transfer belt 5. The toner image is transferred to the recording medium P passing between the transfer belt 5 and the second transfer machine 7 after being transferred to the transfer belt 5. A second transfer bias for transferring the color toner image onto the recording medium P is applied to the second transfer machine 7. The fixing unit 8 applies heat and pressure to the toner image transferred to the recording medium P to fix it to the recording medium P. To this end, the fixing unit 8 includes a pair of fixing rollers 81 and 82 as one embodiment. The heater is built in either or both of the pair of fixing rollers 81 and 82. In this embodiment, a heater is built in the fixing roller 81 which is in contact with the toner layer transferred to the recording medium P. FIG. In the case of the fixing unit 8 used in the color image forming apparatus, a heater is built in both the fixing rollers 81 and 82 in order to effectively melt and fix the thick toner layer.

In the multi-pass method, for example, a yellow electrostatic latent image is formed by using the exposure machine 3 on the image receptor 1 uniformly charged to the image receptor 1. The electrostatic latent image of the image receptor 1 is developed using the developing device 4Y to form a yellow toner image. The yellow toner image is transferred to the transfer belt 5. Next, repeating the above-described process for cyan, magenta and black colors, a color toner image in which four toners of four colors are superimposed on the transfer belt 5 is formed. This color toner image is transferred to the recording medium P. FIG. The fixing unit 8 fixes the color toner image onto the recording medium P. As shown in FIG. As described above, according to the multi-pass image forming apparatus, color printing is realized by forming and fixing a color toner image on the recording medium P through four charging, exposure, developing, and transferring processes.

2 shows another embodiment of an electrophotographic image forming apparatus according to the present invention. The image forming apparatus of this embodiment is a single pass image forming apparatus. As shown in Fig. 2, unlike the multi-pass printing unit 10, the printing unit 10a of this embodiment includes four image receptors 1 and four exposure units 3. Four image receptors 1 are positioned to face the transfer belt 5. Four exposure machines 3 form electrostatic latent images of yellow, cyan, magenta, and black colors on the image receptors 1. The four developing devices 4Y, 4C, 4M, and 4K develop electrostatic latent images of the respective image receptors 1 to form toner images of yellow, cyan, magenta, and black colors on the image receptors 1, respectively. The toner images of each color are sequentially transferred to the transfer belt 5 to form a color toner image in which four toners of four colors are superimposed on the transfer belt 5. This color toner image is transferred to the recording medium P. FIG. The fixing unit 8 fixes the color toner image onto the recording medium P. As shown in FIG. As described above, the single pass type image forming apparatus implements color printing by forming and fixing a color toner image on the recording medium P through a single charging, exposure, developing and transferring process.

1 and 2 illustrate a process of forming an image by a multipath method and a single pass method, and the scope of the present invention is not limited by the configuration of FIGS. 1 and 2.

The toner is made of a base resin, a pigment, a wax, a charge control agent (CCA) as a raw material. These raw materials are mixed in a powder (powder) state and heated, dissolved and kneaded by a kneader. As a kneader, a twin screw extruder, an open roller type kneader, a batch type kneader, etc. are mentioned. The dissolved and kneaded toner is rapidly cooled and solidified by a cooling belt, a cooling roller, or the like. This solidified toner is coarsely ground first. Although the coarse grinder is not specifically limited, Usually, it grinds to about 300 micrometers of average particle diameters. Moreover, when a high performance coarse grinder is used, it can grind | pulverize to about 30 micrometers. The smaller the pulverized particle diameter in this coarse crusher, the smaller the better it is in the range which does not generate | occur | produce a lot of over pulverization, and it can be at least about 15 micrometers. Next, the finely ground powder is pulverized and classified so as to have a predetermined particle size. Next, the finely ground powder is pulverized and classified so as to have a predetermined particle size.

Toner of four colors (yellow, cyan, magenta, black) manufactured in this way is applied to an electrophotographic image forming apparatus and recorded directly or through an intermediate transfer medium by a multipass method or a single pass method as described above. Transferred to a medium forms a color toner image on a recording medium. According to this conventional electrophotographic image forming apparatus, the color toner image is fixed to the recording medium by applying heat and pressure in this state. By forming a transparent toner layer on the color toner image transferred on the recording medium, the present inventors can compensate for the deterioration in image quality due to the thick toner layer to obtain a high quality image.

The transparent toner layer is basically formed on all regions of the recording medium P on the color toner image. In order to form the transparent toner layer, as shown in FIG. 1, the multipath image forming apparatus further includes a developer 4T in which transparent toner is accommodated. Since the transparent toner should be located above the color toner image on the recording medium P, the transparent toner is transferred to the transfer belt 5, and the color toner image is transferred thereon. The single pass type image forming apparatus shown in FIG. 2 further includes a developer 4T in which transparent toner is accommodated, and an exposure machine 3. Similarly, since the transparent toner should be located above the color toner image on the recording medium P, the transparent toner is first transferred to the transfer belt 5, and the color toner image is transferred thereon.

A method of forming a transparent toner layer, comprising: developing a transparent toner in reverse polarity with a toner for forming an image and developing it on an unexposed image receptor 1; charging a transparent toner in the same polarity with a toner for forming an image. There is a method of developing the image receptor 1 on which the entire surface is exposed. In the case of using the transparent toner charged with reverse polarity, it is necessary to optimize the polarity and conditions of the process of transferring to the recording medium P, in particular, the second transfer bias. In the case of using the transparent toner charged with the same polarity, moire should not be generated in the exposure pattern on the image receptor 1.

In either case, in the case of the multipath image forming apparatus, the toner of four colors (or three colors) is usually superposed, and then the transparent toner is coated thereon, so that the coverage is 100%. In the case of the single pass method, the transparent toner is transferred to the transfer belt 5 at the final stage of the transfer process transferred to the transfer belt 5. In the case of the multi-pass method, a color toner image is formed on an intermediate transfer medium such as a transfer belt 5 or a transfer drum (not shown) rather than a transfer method directly to a recording medium P, and then collectively recorded on the recording medium P. In many cases, a method of transferring a card is adopted. Therefore, even if the primary transfer from the image receptor 1 to the intermediate transfer medium is not a problem, the secondary transfer from the intermediate transfer medium to the recording medium P is often worsened. In order to prevent this, an external additive is usually added to the toner to improve the transfer efficiency of the toner. Silica (silica) treated hydrophobic _{surfaces, TiO 2, Al 2 O 3} , polymer beads (polymer beads) of various kinds are typically when combined with an optimum external additive used and the like.

The transparent toner dissolves at the time of fixing and solidifies when the fixing is completed. Transparency after solidification becomes a problem. If the transparency is low, the color image underneath is blurred, and a clear image cannot be obtained. The inventors found out that sufficient image quality can be obtained by securing an average transmittance of 40% or more in the visible region (wavelength 400 nm-700 nm) when the thickness of the transparent toner layer is 10 m after fixing.

However, in the case where the transparent toner layer is formed on the entire surface of the recording medium P, the offset of the transparent toner is fixed to the fixing roller 81 under fixing conditions (fixing temperature and fixing pressure) for sufficiently fixing the color toner image thereunder. (offset) occurs and may not be able to fix. The present inventor solved this problem by making the wax content of a transparent toner higher than a color toner.

Since the color toner layer does not directly contact the roller 81 of the fixing unit 8, the color toner does not necessarily need wax for improving fixability. However, since a small amount of wax helps to improve the dispersibility of the pigment and the charge control agent, when added in the range of 5% or less, the color development and the chargeability are improved.

Proper transparency cannot be secured unless the surface of the transparent toner layer has sufficient smoothness. The inventors found that the smoothness of the surface of the transparent toner layer greatly influences the surface roughness of the roller 81 of the fixing unit 8 in contact with the transparent toner layer. The surface roughness Rz of the roller 81 of the fixing unit 8 in contact with the transparent toner layer needs to be 15 µm or less, and when it is more than that, sufficient transparency cannot be secured.

The inventor also found out that the particle size of the wax added to the transparent toner needs to be 4 µm or less. If the particle size of the wax added to the transparent toner is too large, light is scattered and is not transparent. In addition, in the case where the dispersed particle diameter is too small, particularly in the case of 0.1 µm or less, it cannot contribute to improvement of fixability. Depending on the kneading method of the toner material, the wax particles dispersed in the transparent toner may be elongated instead of spherical. In this case, the dispersed particle diameter is the average of the long and short diameters. Particle size measurement can be performed using the image of a transmission electron microscope.

The inventors found out that high transparency can be obtained when the refractive indexes of the base resin and the wax of the transparent toner are similar to each other. When the refractive index of the base resin constituting the transparent toner is Rr and the refractive index of the wax to be added is Rw, it is important to ensure that the absolute value of the difference in the refractive indices Rr-Rw is 0.2 or less to ensure high transparency.

<Example 1>

Polyester base resins, waxes, pigments, and charge control agents were heated, dissolved, kneaded, pulverized, and classified to prepare color toners having a yellow, cyan, magenta, and black color with an average particle diameter of 8 µm. As the wax, an ester wax having a melting point of 73 ± 2 ° C. was used, and the wax content was 1%. A transparent toner was prepared using a polyester base resin such as a color toner. A wax such as wax added to the color toner was added to the transparent toner, and the content rate was 3.5%. This transparent toner layer had an average transmittance of 55% at a thickness of 10 µm, and was capable of enthusiasm. It was possible to obtain a high quality image with extremely high gloss. The surface roughness of the fixing roller 81 in contact with the transparent toner layer used at this time was 12 m. As a result of observing the cross section of the toner particles with a transmission electron microscope, the wax particles were dispersed in an oval shape, and the particle diameter (average of the long and short diameters) of the wax particles was 2.6 탆. The refractive index of the polyester base resin used at this time was 1.51, and the refractive index of the wax was 1.41.

Comparative Example 1

Polyester base resins, waxes, pigments, and charge control agents were heated, dissolved, kneaded, pulverized, and classified to produce color toners of yellow, cyan, magenta, and black colors having an average particle diameter of 8 µm. As the wax, an ester wax having a melting point of 73 ± 2 ° C. was used, and the wax content was 1%. A transparent toner was prepared using a polyester base resin such as a color toner. A wax such as wax added to the color toner was added to the transparent toner, and the content rate was 1%. Although the average transmittance at this thickness of 10 micrometers of this transparent toner layer was 58%, hot-offset occurred at the time of thermal mounting, and fixing was impossible. As a result of observing the cross section of the toner particles with a transmission electron microscope, the wax particles were dispersed in an elliptical shape, and the particle size (average of the long and short diameters) of the wax particles was 2.8 µm. The refractive index of the polyester base resin used at this time was 1.51, and the refractive index of the wax was 1.41.

Comparative Example 2

Polyester base resins, waxes, pigments, and charge control agents were heated, dissolved, kneaded, pulverized, and classified to produce color toners of yellow, cyan, magenta, and black colors having an average particle diameter of 8 µm. As the wax, an ester wax having a melting point of 73 ± 2 ° C. was used, and the wax content was 1%. Transparent toner was prepared using a polyester base resin such as color toner. A wax such as wax added to the color toner was added to the transparent toner, and the content rate was 3.5%. The surface roughness of the fixing roller 81 in contact with the transparent toner layer was 18 µm. Although passion bonding was possible, the surface roughness of the fixing roller 81 was large and the glossiness of the surface disappeared, and the transmittance was also reduced to 35%. As a result of observing the cross section of the toner particles with a transmission electron microscope, the wax particles were dispersed in an elliptical shape, and the particle diameter (average of the long and short diameters) of the wax particles was 2.6 탆. The refractive index of the polyester base resin used at this time was 1.51, and the refractive index of the wax was 1.41.

Comparative Example 3

Polyester base resins, waxes, pigments, and charge control agents were heated, dissolved, kneaded, pulverized, and classified to produce color toners of yellow, cyan, magenta, and black colors having an average particle diameter of 8 µm. As the wax, an ester wax having a melting point of 73 ± 2 ° C. was used, and the wax content was 1%. A transparent toner was prepared using a polyester base resin such as a color toner. The wax added to the color toner was a polyolefin having a melting point of 120 ± 3 ° C., and the content was 3.5%. The surface roughness of the fixing roller 81 in contact with the transparent toner layer was 12 m. The average transmittance at 10 μm in thickness of this transparent toner layer was 21%. Passion was possible, but the transmittance and glossiness of the image were low. As a result of observing the cross section of the toner particles with a transmission electron microscope, the wax particles were dispersed in an elliptical shape, and the particle diameter (average of the long and short diameters) of the wax particles was 4.8 µm. The refractive index of the polyester base resin used at this time was 1.51, and the refractive index of the wax was 1.27.

As described above, according to the transparent toner of the present invention and the electrophotographic image forming apparatus employing the same, the deterioration of image quality due to the thick toner layer can be compensated by coating the transparent toner on the toner image. In addition, by properly selecting the wax content and the surface roughness of the roller of the fixing machine, it is possible to prevent hot-offset during fixing and to form a transparent toner layer having high transparency.

It is to be understood that the invention is not limited to that described above and illustrated in the drawings, and that more modifications and variations are possible within the scope of the following claims.

Claims (7)

A transparent toner for an electrophotographic image forming apparatus which is superimposed and fixed together on a toner image forming a print image, A transparent toner of an electrophotographic image forming apparatus, comprising a base resin, a wax, and a charge control agent, wherein the content of the wax is higher than that of the toner forming the printed image. The method of claim 1, The transparent toner of the electrophotographic image forming apparatus, wherein the average transmittance of the visible region is 40% or more when the thickness is 10 m. The method according to claim 1 or 2, The transparent toner of the electrophotographic image forming apparatus, wherein an average particle diameter of the wax particles is 4 µm or less. The method of claim 3, A transparent toner of an electrophotographic image forming apparatus, wherein an absolute value of a difference between the refractive index of the base resin and the refractive orange of the wax is 0.2 or less. An electrophotographic method comprising a printing unit for forming a toner image of at least one color on a recording medium by an electrophotographic method, coating a transparent toner thereon, and a fixing unit for fixing the toner image and the transparent toner by applying heat and pressure thereto; In the image forming apparatus, The surface roughness of the roller in contact with the transparent toner of the fixing unit is Rz 15㎛ or less, characterized in that the electrophotographic image forming apparatus. The method of claim 5, The transparent toner has an average transmittance of 40% or more in the visible region when the thickness is 10 μm, the wax content is higher than the wax content of the toner forming the toner image, and the average particle diameter of the wax particles is 4 μm or less. An electrophotographic image forming apparatus. The method of claim 6, The absolute value of the difference between the refractive index of the base resin of the transparent toner and the refractive orange of the wax is 0.2 or less.

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